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Porter SS, Dupin SE, Denison RF, Kiers ET, Sachs JL. Host-imposed control mechanisms in legume-rhizobia symbiosis. Nat Microbiol 2024:10.1038/s41564-024-01762-2. [PMID: 39095495 DOI: 10.1038/s41564-024-01762-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 06/17/2024] [Indexed: 08/04/2024]
Abstract
Legumes are ecologically and economically important plants that contribute to nutrient cycling and agricultural sustainability, features tied to their intimate symbiosis with nitrogen-fixing rhizobia. Rhizobia vary dramatically in quality, ranging from highly growth-promoting to non-beneficial; therefore, legumes must optimize their symbiosis with rhizobia through host mechanisms that select for beneficial rhizobia and limit losses to non-beneficial strains. In this Perspective, we examine the considerable scientific progress made in decoding host control over rhizobia, empirically examining both molecular and cellular mechanisms and their effects on rhizobia symbiosis and its benefits. We consider pre-infection controls, which require the production and detection of precise molecular signals by the legume to attract and select for compatible rhizobia strains. We also discuss post-infection mechanisms that leverage the nodule-level and cell-level compartmentalization of symbionts to enable host control over rhizobia development and proliferation in planta. These layers of host control each contribute to legume fitness by directing host resources towards a narrowing subset of more-beneficial rhizobia.
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Affiliation(s)
- Stephanie S Porter
- School of Biological Sciences, Washington State University, Vancouver, WA, USA
| | - Simon E Dupin
- Amsterdam Institute for Life and Environment, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
| | - R Ford Denison
- Department of Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, MN, USA
| | - E Toby Kiers
- Amsterdam Institute for Life and Environment, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
| | - Joel L Sachs
- Department of Evolution, Ecology and Organismal Biology, University of California, Riverside, CA, USA.
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2
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Gtari M, Beauchemin NJ, Sarker I, Sen A, Ghodhbane-Gtari F, Tisa LS. An overview of Parafrankia (Nod+/Fix+) and Pseudofrankia (Nod+/Fix-) interactions through genome mining and experimental modeling in co-culture and co-inoculation of Elaeagnus angustifolia. Appl Environ Microbiol 2024; 90:e0028824. [PMID: 38651928 PMCID: PMC11107149 DOI: 10.1128/aem.00288-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2024] [Accepted: 04/02/2024] [Indexed: 04/25/2024] Open
Abstract
In many frankia, the ability to nodulate host plants (Nod+) and fix nitrogen (Fix+) is a common strategy. However, some frankia within the Pseudofrankia genus lack one or two of these traits. This phenomenon has been consistently observed across various actinorhizal nodule isolates, displaying Nod- and/or Fix- phenotypes. Yet, the mechanisms supporting the colonization and persistence of these inefficient frankia within nodules, both with and without symbiotic strains (Nod+/Fix+), remain unclear. It is also uncertain whether these associations burden or benefit host plants. This study delves into the ecological interactions between Parafrankia EUN1f and Pseudofrankia inefficax EuI1c, isolated from Elaeagnus umbellata nodules. EUN1f (Nod+/Fix+) and EuI1c (Nod+/Fix-) display contrasting symbiotic traits. While the prediction suggests a competitive scenario, the absence of direct interaction evidence implies that the competitive advantage of EUN1f and EuI1c is likely contingent on contextual factors such as substrate availability and the specific nature of stressors in their respective habitats. In co-culture, EUN1f outperforms EuI1c, especially under specific conditions, driven by its nitrogenase activity. Iron-depleted conditions favor EUN1f, emphasizing iron's role in microbial competition. Both strains benefit from host root exudates in pure culture, but EUN1f dominates in co-culture, enhancing its competitive traits. Nodulation experiments show that host plant preferences align with inoculum strain abundance under nitrogen-depleted conditions, while consistently favoring EUN1f in nitrogen-supplied media. This study unveils competitive dynamics and niche exclusion between EUN1f and EuI1c, suggesting that host plant may penalize less effective strains and even all strains. These findings highlight the complex interplay between strain competition and host selective pressure, warranting further research into the underlying mechanisms shaping plant-microbe-microbe interactions in diverse ecosystems. IMPORTANCE While Pseudofrankia strains typically lack the common traits of ability to nodulate the host plant (Nod-) and/or fix nitrogen (Fix-), they are still recovered from actinorhizal nodules. The enigmatic question of how and why these unconventional strains establish themselves within nodule tissue, thriving either alongside symbiotic strains (Nod+/Fix+) or independently, while considering potential metabolic costs to the host plant, remains a perplexing puzzle. This study endeavors to unravel the competitive dynamics between Pseudofrankia inefficax strain EuI1c (Nod+/Fix-) and Parafrankia strain EU1Nf (Nod+/Fix+) through a comprehensive exploration of genomic data and empirical modeling, conducted both in controlled laboratory settings and within the host plant environment.
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Affiliation(s)
- Maher Gtari
- Department of Biological and Chemical Engineering USCR Molecular Bacteriology and Genomics, National Institute of Applied Sciences and Technology, University of Carthage, Carthage, Tunisia
| | - Nicholas J. Beauchemin
- Department of Molecular, Cellular, and Biomedical Sciences, University of New Hampshire, Durham, New Hampshire, USA
| | - Indrani Sarker
- Bioinformatics Facility, University of North Bengal, Raja Rammohanpur, Siliguri, West Bengal, India
| | - Arnab Sen
- Bioinformatics Facility, University of North Bengal, Raja Rammohanpur, Siliguri, West Bengal, India
| | - Faten Ghodhbane-Gtari
- Department of Biological and Chemical Engineering USCR Molecular Bacteriology and Genomics, National Institute of Applied Sciences and Technology, University of Carthage, Carthage, Tunisia
- Higher Institute of Biotechnology of Sidi Thabet, University of La Manouba, Sidi Thabet, Tunisia
| | - Louis S. Tisa
- Department of Molecular, Cellular, and Biomedical Sciences, University of New Hampshire, Durham, New Hampshire, USA
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3
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Reichman JR, Slattery MR, Johnson MG, Andersen CP, Harper SL. CeO 2 nanoparticle dose and exposure modulate soybean development and plant-mediated responses in root-associated bacterial communities. Sci Rep 2024; 14:10231. [PMID: 38702407 PMCID: PMC11068890 DOI: 10.1038/s41598-024-60344-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2023] [Accepted: 04/22/2024] [Indexed: 05/06/2024] Open
Abstract
Agricultural soils are increasingly undergoing inadvertent and purposeful exposures to engineered CeO2 nanoparticles (NPs), which can impact crops and root-associated microbial communities. However, interactions between NP concentration and exposure duration on plant-mediated responses of root-associated bacterial communities are not well understood. Soybeans seedlings were grown in soil with uncoated NPs added at concentrations of 0, 1 or 100 mg kg-1. Total soil exposure durations were either 190 days, starting 106 days before planting or 84 days with NP amendments coinciding with planting. We assessed plant development, bacterial diversity, differential abundance and inferred functional changes across rhizosphere, rhizoplane, and root tissue compartments. Plant non-monotonic dose responses were mirrored in bacterial communities. Most notably, effects were magnified in the rhizoplane under low-dose, short-exposures. Enriched metabolic pathways were primarily related to biosynthesis and degradation/utilization/assimilation, rather than responses to metals or oxidative stress. Our results indicate that plant-mediated bacterial responses were greater than direct NP impacts. Also, we identify needs for modeling non-monotonic legume stress responses that account for coinfection with mutualistic and parasitic bacteroids. Our findings provide new insights regarding effects of applications of soil amendments such as biosolids containing NPs or nano-enabled formulations used in cultivation of legumes and other crops.
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Affiliation(s)
- Jay R Reichman
- Pacific Ecological Systems Division, Office of Research and Development, US Environmental Protection Agency, Corvallis, OR, 97333, USA.
- Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, OR, 97331, USA.
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, 97331, USA.
| | - Matthew R Slattery
- Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, OR, 97331, USA
| | - Mark G Johnson
- Pacific Ecological Systems Division, Office of Research and Development, US Environmental Protection Agency, Corvallis, OR, 97333, USA
| | - Christian P Andersen
- Pacific Ecological Systems Division, Office of Research and Development, US Environmental Protection Agency, Corvallis, OR, 97333, USA
| | - Stacey L Harper
- Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, OR, 97331, USA
- School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, OR, 97331, USA
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Karasev ES, Hosid SL, Aksenova TS, Onishchuk OP, Kurchak ON, Dzyubenko NI, Andronov EE, Provorov NA. Impacts of Natural Selection on Evolution of Core and Symbiotically Specialized ( sym) Genes in the Polytypic Species Neorhizobium galegae. Int J Mol Sci 2023; 24:16696. [PMID: 38069024 PMCID: PMC10706768 DOI: 10.3390/ijms242316696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Revised: 11/17/2023] [Accepted: 11/20/2023] [Indexed: 12/18/2023] Open
Abstract
Nodule bacteria (rhizobia) represent a suitable model to address a range of fundamental genetic problems, including the impacts of natural selection on the evolution of symbiotic microorganisms. Rhizobia possess multipartite genomes in which symbiotically specialized (sym) genes differ from core genes in their natural histories. Diversification of sym genes is responsible for rhizobia microevolution, which depends on host-induced natural selection. By contrast, diversification of core genes is responsible for rhizobia speciation, which occurs under the impacts of still unknown selective factors. In this paper, we demonstrate that in goat's rue rhizobia (Neorhizobium galegae) populations collected at North Caucasus, representing two host-specific biovars orientalis and officianalis (N2-fixing symbionts of Galega orientalis and G. officinalis), the evolutionary mechanisms are different for core and sym genes. In both N. galegae biovars, core genes are more polymorphic than sym genes. In bv. orientalis, the evolution of core genes occurs under the impacts of driving selection (dN/dS > 1), while the evolution of sym genes is close to neutral (dN/dS ≈ 1). In bv. officinalis, the evolution of core genes is neutral, while for sym genes, it is dependent on purifying selection (dN/dS < 1). A marked phylogenetic congruence of core and sym genes revealed using ANI analysis may be due to a low intensity of gene transfer within and between N. galegae biovars. Polymorphism in both gene groups and the impacts of driving selection on core gene evolution are more pronounced in bv. orientalis than in bv. officianalis, reflecting the diversities of their respective host plant species. In bv. orientalis, a highly significant (P0 < 0.001) positive correlation is revealed between the p-distance and dN/dS values for core genes, while in bv. officinalis, this correlation is of low significance (0.05 < P0 < 0.10). For sym genes, the correlation between p-distance and dN/dS values is negative in bv. officinalis but is not revealed in bv. orientalis. These data, along with the functional annotation of core genes implemented using Gene Ontology tools, suggest that the evolution of bv. officinalis is based mostly on adaptation for in planta niches while in bv. orientalis, evolution presumably depends on adaptation for soil niches. New insights into the tradeoff between natural selection and genetic diversity are presented, suggesting that gene nucleotide polymorphism may be extended by driving selection only in ecologically versatile organisms capable of supporting a broad spectrum of gene alleles in their gene pools.
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Affiliation(s)
- Evgeny S. Karasev
- All-Russia Research Institute for Agricultural Microbiology, 196608 St. Petersburg, Russia; (E.S.K.); (S.L.H.); (T.S.A.); (O.P.O.); (O.N.K.); (N.A.P.)
| | - Sergey L. Hosid
- All-Russia Research Institute for Agricultural Microbiology, 196608 St. Petersburg, Russia; (E.S.K.); (S.L.H.); (T.S.A.); (O.P.O.); (O.N.K.); (N.A.P.)
| | - Tatiana S. Aksenova
- All-Russia Research Institute for Agricultural Microbiology, 196608 St. Petersburg, Russia; (E.S.K.); (S.L.H.); (T.S.A.); (O.P.O.); (O.N.K.); (N.A.P.)
| | - Olga P. Onishchuk
- All-Russia Research Institute for Agricultural Microbiology, 196608 St. Petersburg, Russia; (E.S.K.); (S.L.H.); (T.S.A.); (O.P.O.); (O.N.K.); (N.A.P.)
| | - Oksana N. Kurchak
- All-Russia Research Institute for Agricultural Microbiology, 196608 St. Petersburg, Russia; (E.S.K.); (S.L.H.); (T.S.A.); (O.P.O.); (O.N.K.); (N.A.P.)
| | - Nikolay I. Dzyubenko
- All-Russia Research Institute of Plant Genetic Resources, 190031 St. Petersburg, Russia;
| | - Evgeny E. Andronov
- All-Russia Research Institute for Agricultural Microbiology, 196608 St. Petersburg, Russia; (E.S.K.); (S.L.H.); (T.S.A.); (O.P.O.); (O.N.K.); (N.A.P.)
- Dokuchaev Soil Science Institute, 119017 Moscow, Russia
| | - Nikolay A. Provorov
- All-Russia Research Institute for Agricultural Microbiology, 196608 St. Petersburg, Russia; (E.S.K.); (S.L.H.); (T.S.A.); (O.P.O.); (O.N.K.); (N.A.P.)
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5
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Granada Agudelo M, Ruiz B, Capela D, Remigi P. The role of microbial interactions on rhizobial fitness. FRONTIERS IN PLANT SCIENCE 2023; 14:1277262. [PMID: 37877089 PMCID: PMC10591227 DOI: 10.3389/fpls.2023.1277262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Accepted: 09/22/2023] [Indexed: 10/26/2023]
Abstract
Rhizobia are soil bacteria that can establish a nitrogen-fixing symbiosis with legume plants. As horizontally transmitted symbionts, the life cycle of rhizobia includes a free-living phase in the soil and a plant-associated symbiotic phase. Throughout this life cycle, rhizobia are exposed to a myriad of other microorganisms that interact with them, modulating their fitness and symbiotic performance. In this review, we describe the diversity of interactions between rhizobia and other microorganisms that can occur in the rhizosphere, during the initiation of nodulation, and within nodules. Some of these rhizobia-microbe interactions are indirect, and occur when the presence of some microbes modifies plant physiology in a way that feeds back on rhizobial fitness. We further describe how these interactions can impose significant selective pressures on rhizobia and modify their evolutionary trajectories. More extensive investigations on the eco-evolutionary dynamics of rhizobia in complex biotic environments will likely reveal fascinating new aspects of this well-studied symbiotic interaction and provide critical knowledge for future agronomical applications.
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Affiliation(s)
- Margarita Granada Agudelo
- Laboratoire des Interactions Plantes Microbes Environnement (LIPME), Université de Toulouse, INRAE, CNRS, Castanet-Tolosan, France
| | - Bryan Ruiz
- Laboratoire des Interactions Plantes Microbes Environnement (LIPME), Université de Toulouse, INRAE, CNRS, Castanet-Tolosan, France
| | - Delphine Capela
- Laboratoire des Interactions Plantes Microbes Environnement (LIPME), Université de Toulouse, INRAE, CNRS, Castanet-Tolosan, France
| | - Philippe Remigi
- Laboratoire des Interactions Plantes Microbes Environnement (LIPME), Université de Toulouse, INRAE, CNRS, Castanet-Tolosan, France
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6
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Mohd-Radzman NA, Drapek C. Compartmentalisation: A strategy for optimising symbiosis and tradeoff management. PLANT, CELL & ENVIRONMENT 2023; 46:2998-3011. [PMID: 36717758 DOI: 10.1111/pce.14553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2022] [Revised: 01/19/2023] [Accepted: 01/26/2023] [Indexed: 06/18/2023]
Abstract
Plant root architecture is developmentally plastic in response to fluctuating nutrient levels in the soil. Part of this developmental plasticity is the formation of dedicated root cells and organs to host mutualistic symbionts. Structures like nitrogen-fixing nodules serve as alternative nutrient acquisition strategies during starvation conditions. Some root systems can also form myconodules-globular root structures that can host mycorrhizal fungi. The myconodule association is different from the wide-spread arbuscular mycorrhization. This range of symbiotic associations provides different degrees of compartmentalisation, from the cellular to organ scale, which allows the plant host to regulate the entry and extent of symbiotic interactions. In this review, we discuss the degrees of symbiont compartmentalisation by the plant host as a developmental strategy and speculate how spatial confinement mitigates risks associated with root symbiosis.
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Affiliation(s)
| | - Colleen Drapek
- Sainsbury Laboratory Cambridge University (SLCU), Bateman Street, Cambridge, UK
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7
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Holland BL, Matthews ML, Bota P, Sweetlove LJ, Long SP, diCenzo GC. A genome-scale metabolic reconstruction of soybean and Bradyrhizobium diazoefficiens reveals the cost-benefit of nitrogen fixation. THE NEW PHYTOLOGIST 2023; 240:744-756. [PMID: 37649265 DOI: 10.1111/nph.19203] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Accepted: 07/05/2023] [Indexed: 09/01/2023]
Abstract
Nitrogen-fixing symbioses allow legumes to thrive in nitrogen-poor soils at the cost of diverting some photoassimilate to their microsymbionts. Effort is being made to bioengineer nitrogen fixation into nonleguminous crops. This requires a quantitative understanding of its energetic costs and the links between metabolic variations and symbiotic efficiency. A whole-plant metabolic model for soybean (Glycine max) with its associated microsymbiont Bradyrhizobium diazoefficiens was developed and applied to predict the cost-benefit of nitrogen fixation with varying soil nitrogen availability. The model predicted a nitrogen-fixation cost of c. 4.13 g C g-1 N, which when implemented into a crop scale model, translated to a grain yield reduction of 27% compared with a non-nodulating plant receiving its nitrogen from the soil. Considering the lower nitrogen content of cereals, the yield cost to a hypothetical N-fixing cereal is predicted to be less than half that of soybean. Soybean growth was predicted to be c. 5% greater when the nodule nitrogen export products were amides versus ureides. This is the first metabolic reconstruction in a tropical crop species that simulates the entire plant and nodule metabolism. Going forward, this model will serve as a tool to investigate carbon use efficiency and key mechanisms within N-fixing symbiosis in a tropical species forming determinate nodules.
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Affiliation(s)
- Bethany L Holland
- Carl R Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Megan L Matthews
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Pedro Bota
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK
| | - Lee J Sweetlove
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK
| | - Stephen P Long
- Carl R Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- Departments of Plant Biology and of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - George C diCenzo
- Department of Biology, Queen's University, Kingston, ON, K7L 3N6, Canada
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Rahman A, Manci M, Nadon C, Perez IA, Farsamin WF, Lampe MT, Le TH, Torres Martínez L, Weisberg AJ, Chang JH, Sachs JL. Competitive interference among rhizobia reduces benefits to hosts. Curr Biol 2023; 33:2988-3001.e4. [PMID: 37490853 DOI: 10.1016/j.cub.2023.06.081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Revised: 03/31/2023] [Accepted: 06/29/2023] [Indexed: 07/27/2023]
Abstract
The capacity of beneficial microbes to compete for host infection-and the ability of hosts to discriminate among them-introduces evolutionary conflict that is predicted to destabilize mutualism. We investigated fitness outcomes in associations between legumes and their symbiotic rhizobia to characterize fitness impacts of microbial competition. Diverse Bradyrhizobium strains varying in their capacity to fix nitrogen symbiotically with a common host plant, Acmispon strigosus, were tested in full-factorial coinoculation experiments involving 28 pairwise strain combinations. We analyzed the effects of interstrain competition and host discrimination on symbiotic-interaction outcomes by relativizing fitness proxies to clonally infected and uninfected controls. More than one thousand root nodules of coinoculated plants were genotyped to quantify strain occupancy, and the Bradyrhizobium strain genome sequences were analyzed to uncover the genetic bases of interstrain competition outcomes. Strikingly, interstrain competition favored a fast-growing, minimally beneficial rhizobia strain. Host benefits were significantly diminished in coinoculation treatments relative to expectations from clonally inoculated controls, consistent with competitive interference among rhizobia that reduced both nodulation and plant growth. Competition traits appear polygenic, linked with inter-strain allelopathic interactions in the rhizosphere. This study confirms that competition among strains can destabilize mutualism by favoring microbes that are superior in colonizing host tissues but provide minimal benefits to host plants. Moreover, our findings help resolve the paradox that despite efficient host control post infection, legumes nonetheless encounter rhizobia that vary in their nitrogen fixation.
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Affiliation(s)
- Arafat Rahman
- Institute of Integrative Genome Biology, University of California, Riverside, Riverside, CA 92521, USA
| | - Max Manci
- Department of Microbiology & Plant Pathology, University of California, Riverside, Riverside, CA 92521, USA
| | - Cassandra Nadon
- Department of Evolution Ecology & Organismal Biology, University of California, Riverside, Riverside, CA 92521, USA
| | - Ivan A Perez
- Department of Evolution Ecology & Organismal Biology, University of California, Riverside, Riverside, CA 92521, USA
| | - Warisha F Farsamin
- Department of Evolution Ecology & Organismal Biology, University of California, Riverside, Riverside, CA 92521, USA
| | - Matthew T Lampe
- Department of Evolution Ecology & Organismal Biology, University of California, Riverside, Riverside, CA 92521, USA
| | - Tram H Le
- Department of Evolution Ecology & Organismal Biology, University of California, Riverside, Riverside, CA 92521, USA
| | - Lorena Torres Martínez
- Department of Evolution Ecology & Organismal Biology, University of California, Riverside, Riverside, CA 92521, USA; Department of Biology, St. Mary's College of Maryland, St. Mary's City, MD 20686, USA
| | - Alexandra J Weisberg
- Department of Botany & Plant Pathology, Oregon State University, Corvallis, OR 97331, USA
| | - Jeff H Chang
- Department of Botany & Plant Pathology, Oregon State University, Corvallis, OR 97331, USA
| | - Joel L Sachs
- Institute of Integrative Genome Biology, University of California, Riverside, Riverside, CA 92521, USA; Department of Microbiology & Plant Pathology, University of California, Riverside, Riverside, CA 92521, USA; Department of Evolution Ecology & Organismal Biology, University of California, Riverside, Riverside, CA 92521, USA.
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9
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Burghardt LT, diCenzo GC. The evolutionary ecology of rhizobia: multiple facets of competition before, during, and after symbiosis with legumes. Curr Opin Microbiol 2023; 72:102281. [PMID: 36848712 DOI: 10.1016/j.mib.2023.102281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2022] [Revised: 01/12/2023] [Accepted: 01/20/2023] [Indexed: 02/27/2023]
Abstract
Rhizobial bacteria have complex lifestyles that involve growth and survival in bulk soil, plant rhizospheres and rhizoplanes, legume infection threads, and mature and senescing legume nodules. In nature, rhizobia coexist and compete with many other rhizobial strains and species to form host associations. We review recent work defining competitive interactions across these environments. We highlight the use of sophisticated measurement tools and sequencing technologies to examine competition mechanisms in planta, and highlight environments (e.g. soil and senescing nodules) where we still know exceedingly little. We argue that moving toward an explicitly ecological framework (types of competition, resources, and genetic differentiation) will clarify the evolutionary ecology of these foundational organisms and open doors for engineering sustainable, beneficial associations with hosts.
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Affiliation(s)
- Liana T Burghardt
- The Pennsylvania State University, Department of Plant Science, University Park, PA 16802, United States; The Pennsylvania State University, Ecology Graduate Program, University Park, PA 16802, United States.
| | - George C diCenzo
- Queen's University, Department of Biology, Kingston, ON K7L 3N6, Canada
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10
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Quides KW, Lee Y, Hur T, Atamian HS. Evaluation of qPCR to Detect Shifts in Population Composition of the Rhizobial Symbiont Mesorhizobium japonicum during Serial in Planta Transfers. BIOLOGY 2023; 12:biology12020277. [PMID: 36829553 PMCID: PMC9953586 DOI: 10.3390/biology12020277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Revised: 01/25/2023] [Accepted: 01/31/2023] [Indexed: 02/12/2023]
Abstract
Microbial symbionts range from mutualistic to commensal to antagonistic. While these roles are distinct in their outcome, they are also fluid in a changing environment. Here, we used the Lotus japonicus-Mesorhizobium japonicum symbiosis to investigate short-term and long-term shifts in population abundance using an effective, fast, and low-cost tracking methodology for M. japonicum. We use quantitative polymerase chain reaction (qPCR) to track previously generated signature-tagged M. japonicum mutants targeting the Tn5 transposon insertion and the flanking gene. We used a highly beneficial wild type and moderately beneficial and non-beneficial mutants of M. japonicum sp. nov. to demonstrate the specificity of these primers to estimate the relative abundance of each genotype within individual nodules and after serial transfers to new hosts. For the moderate and non-beneficial genotypes, qPCR allowed us to differentiate genotypes that are phenotypically indistinguishable and investigate host control with suboptimal symbionts. We consistently found the wild type increasing in the proportion of the population, but our data suggest a potential reproductive trade-off between the moderate and non-beneficial genotypes. The multi-generation framework we used, coupled with qPCR, can easily be scaled up to track dozens of M. japonicum mutants simultaneously. Moreover, these mutants can be used to explore M. japonicum genotype abundance in the presence of a complex soil community.
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Affiliation(s)
- Kenjiro W. Quides
- Biological Sciences Program, Schmid College of Science and Technology, Chapman University, Orange, CA 92866, USA
- Department of Microbiology and Molecular Genetics, University of California, Davis, CA 95616, USA
| | - Yoobeen Lee
- Biological Sciences Program, Schmid College of Science and Technology, Chapman University, Orange, CA 92866, USA
| | - Teresa Hur
- Biological Sciences Program, Schmid College of Science and Technology, Chapman University, Orange, CA 92866, USA
| | - Hagop S. Atamian
- Biological Sciences Program, Schmid College of Science and Technology, Chapman University, Orange, CA 92866, USA
- Correspondence:
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11
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Montoya AP, Wendlandt CE, Benedict AB, Roberts M, Piovia-Scott J, Griffitts JS, Porter SS. Hosts winnow symbionts with multiple layers of absolute and conditional discrimination mechanisms. Proc Biol Sci 2023; 290:20222153. [PMID: 36598018 PMCID: PMC9811631 DOI: 10.1098/rspb.2022.2153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
In mutualism, hosts select symbionts via partner choice and preferentially direct more resources to symbionts that provide greater benefits via sanctions. At the initiation of symbiosis, prior to resource exchange, it is not known how the presence of multiple symbiont options (i.e. the symbiont social environment) impacts partner choice outcomes. Furthermore, little research addresses whether hosts primarily discriminate among symbionts via sanctions, partner choice or a combination. We inoculated the legume, Acmispon wrangelianus, with 28 pairs of fluorescently labelled Mesorhizobium strains that vary continuously in quality as nitrogen-fixing symbionts. We find that hosts exert robust partner choice, which enhances their fitness. This partner choice is conditional such that a strain's success in initiating nodules is impacted by other strains in the social environment. This social genetic effect is as important as a strain's own genotype in determining nodulation and has both transitive (consistent) and intransitive (idiosyncratic) effects on the probability that a symbiont will form a nodule. Furthermore, both absolute and conditional partner choice act in concert with sanctions, among and within nodules. Thus, multiple forms of host discrimination act as a series of sieves that optimize host benefits and select for costly symbiont cooperation in mixed symbiont populations.
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Affiliation(s)
- Angeliqua P. Montoya
- School of Biological Sciences, Washington State University, Vancouver, WA 98686, USA
| | - Camille E. Wendlandt
- School of Biological Sciences, Washington State University, Vancouver, WA 98686, USA
| | - Alex B. Benedict
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA
| | - Miles Roberts
- School of Biological Sciences, Washington State University, Vancouver, WA 98686, USA
| | - Jonah Piovia-Scott
- School of Biological Sciences, Washington State University, Vancouver, WA 98686, USA
| | - Joel S. Griffitts
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA
| | - Stephanie S. Porter
- School of Biological Sciences, Washington State University, Vancouver, WA 98686, USA
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12
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Klein M, Stewart JD, Porter SS, Weedon JT, Kiers ET. Evolution of manipulative microbial behaviors in the rhizosphere. Evol Appl 2022; 15:1521-1536. [PMID: 36330300 PMCID: PMC9624083 DOI: 10.1111/eva.13333] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 11/30/2021] [Accepted: 12/02/2021] [Indexed: 01/01/2023] Open
Abstract
The rhizosphere has been called "one of the most complex ecosystems on earth" because it is a hotspot for interactions among millions of microbial cells. Many of these are microbes are also participating in a dynamic interplay with host plant tissues, signaling pathways, and metabolites. Historically, breeders have employed a plant-centric perspective when trying to harness the potential of microbiome-derived benefits to improve productivity and resilience of economically important plants. This is potentially problematic because: (i) the evolution of the microbes themselves is often ignored, and (ii) it assumes that the fitness of interacting plants and microbes is strictly aligned. In contrast, a microbe-centric perspective recognizes that putatively beneficial microbes are still under selection to increase their own fitness, even if there are costs to the host. This can lead to the evolution of sophisticated, potentially subtle, ways for microbes to manipulate the phenotype of their hosts, as well as other microbes in the rhizosphere. We illustrate this idea with a review of cases where rhizosphere microbes have been demonstrated to directly manipulate host root growth, architecture and exudation, host nutrient uptake systems, and host immunity and defense. We also discuss indirect effects, whereby fitness outcomes for the plant are a consequence of ecological interactions between rhizosphere microbes. If these consequences are positive for the plant, they can potentially be misconstrued as traits that have evolved to promote host growth, even if they are a result of selection for unrelated functions. The ubiquity of both direct microbial manipulation of hosts and context-dependent, variable indirect effects leads us to argue that an evolutionary perspective on rhizosphere microbial ecology will become increasingly important as we continue to engineer microbial communities for crop production.
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Affiliation(s)
- Malin Klein
- Department of Ecological ScienceVrije Universiteit AmsterdamAmsterdamThe Netherlands
| | - Justin D. Stewart
- Department of Ecological ScienceVrije Universiteit AmsterdamAmsterdamThe Netherlands
| | - Stephanie S. Porter
- School of Biological SciencesWashington State UniversityVancouverWashingtonUSA
| | - James T. Weedon
- Department of Ecological ScienceVrije Universiteit AmsterdamAmsterdamThe Netherlands
| | - E. Toby Kiers
- Department of Ecological ScienceVrije Universiteit AmsterdamAmsterdamThe Netherlands
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13
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Denison RF, Muller KE. An evolutionary perspective on increasing net benefits to crops from symbiotic microbes. Evol Appl 2022; 15:1490-1504. [PMID: 36330301 PMCID: PMC9624085 DOI: 10.1111/eva.13384] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 04/05/2022] [Accepted: 04/06/2022] [Indexed: 11/30/2022] Open
Abstract
Plant-imposed, fitness-reducing sanctions against less-beneficial symbionts have been documented for rhizobia, mycorrhizal fungi, and fig wasps. Although most of our examples are for rhizobia, we argue that the evolutionary persistence of mutualism in any symbiosis would require such sanctions, if there are multiple symbiont genotypes per host plant. We therefore discuss methods that could be used to develop and assess crops with stricter sanctions. These include methods to screen strains for greater mutualism as resources to identify crop genotypes that impose stronger selection for mutualism. Single-strain experiments that measure costs as well as benefits have shown that diversion of resources by rhizobia can reduce nitrogen-fixation efficiency (N per C) and that some legumes can increase this efficiency by manipulating their symbionts. Plants in the field always host multiple strains with possible synergistic interactions, so benefits from different strains might best be compared by regressing plant growth or yield on each strain's abundance in a mixture. However, results from this approach have not yet been published. To measure legacy effects of stronger sanctions on future crops, single-genotype test crops could be planted in a field that recently had replicated plots with different genotypes of the sanction-imposing crop. Enhancing agricultural benefits from symbiosis may require accepting tradeoffs that constrained past natural selection, including tradeoffs between current and future benefits.
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Affiliation(s)
- R. Ford Denison
- Ecology, Evolution, & BehaviorUniversity of MinnesotaSaint PaulMinnesotaUSA
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14
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Mathesius U. Are legumes different? Origins and consequences of evolving nitrogen fixing symbioses. JOURNAL OF PLANT PHYSIOLOGY 2022; 276:153765. [PMID: 35952452 DOI: 10.1016/j.jplph.2022.153765] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 07/01/2022] [Accepted: 07/03/2022] [Indexed: 05/14/2023]
Abstract
Nitrogen fixing symbioses between plants and bacteria are ancient and, while not numerous, are formed in diverse lineages of plants ranging from microalgae to angiosperms. One symbiosis stands out as the most widespread one is that between legumes and rhizobia, leading to the formation of nitrogen-fixing nodules. The legume family is one of the largest and most diverse group of plants and legumes have been used by humans since the beginning of agriculture, both as high nitrogen food, as well as pastures and rotation crops. One open question is whether their ability to form a nitrogen-fixing symbiosis has contributed to legumes' success, and whether legumes have any unique characteristics that have made them more diverse and widespread than other groups of plants. This review examines the evolutionary journey that has led to the diversification of legumes, in particular its nitrogen-fixing symbiosis, and asks four questions to investigate which legume traits might have contributed to their success: 1. In what ways do legumes differ from other plant groups that have evolved nitrogen-fixing symbioses? In order to answer this question, the characteristics of the symbioses, and efficiencies of nitrogen fixation are compared between different groups of nitrogen fixing plants. 2. Could certain unique features of legumes be a reason for their success? This section examines the manifestations and possible benefits of a nitrogen-rich 'lifestyle' in legumes. 3. If nitrogen fixation was a reason for such a success, why have some species lost the symbiosis? Formation of symbioses has trade-offs, and while these are less well known for non-legumes, there are known energetic and ecological reasons for loss of symbiotic potential in legumes. 4. What can we learn from the unique traits of legumes for future crop improvements? While exploiting some of the physiological properties of legumes could be used to improve legume breeding, our increasing molecular understanding of the essential regulators of root nodule symbioses raise hope of creating new nitrogen fixing symbioses in other crop species.
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Affiliation(s)
- Ulrike Mathesius
- Division of Plant Sciences, Research School of Biology, The Australian National University, 134 Linnaeus Way, Canberra, ACT, 2601, Australia.
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15
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Batstone RT, Burghardt LT, Heath KD. Phenotypic and genomic signatures of interspecies cooperation and conflict in naturally occurring isolates of a model plant symbiont. Proc Biol Sci 2022; 289:20220477. [PMID: 35858063 PMCID: PMC9277234 DOI: 10.1098/rspb.2022.0477] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Given the need to predict the outcomes of (co)evolution in host-associated microbiomes, whether microbial and host fitnesses tend to trade-off, generating conflict, remains a pressing question. Examining the relationships between host and microbe fitness proxies at both the phenotypic and genomic levels can illuminate the mechanisms underlying interspecies cooperation and conflict. We examined naturally occurring genetic variation in 191 strains of the model microbial symbiont Sinorhizobium meliloti, paired with each of two host Medicago truncatula genotypes in single- or multi-strain experiments to determine how multiple proxies of microbial and host fitness were related to one another and test key predictions about mutualism evolution at the genomic scale, while also addressing the challenge of measuring microbial fitness. We found little evidence for interspecies fitness conflict; loci tended to have concordant effects on both microbe and host fitnesses, even in environments with multiple co-occurring strains. Our results emphasize the importance of quantifying microbial relative fitness for understanding microbiome evolution and thus harnessing microbiomes to improve host fitness. Additionally, we find that mutualistic coevolution between hosts and microbes acts to maintain, rather than erode, genetic diversity, potentially explaining why variation in mutualism traits persists in nature.
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Affiliation(s)
- Rebecca T. Batstone
- Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, 1206 West Gregory Drive, Urbana, IL 61801, USA
| | - Liana T. Burghardt
- Department of Plant Science, The Pennsylvania State University, 103 Tyson Building, University Park, PA, 16802 USA
| | - Katy D. Heath
- Department of Plant Biology, University of Illinois at Urbana-Champaign, 286 Morrill Hall, 505 South Goodwin Avenue, Urbana, IL 61801, USA
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16
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Epstein B, Burghardt LT, Heath KD, Grillo MA, Kostanecki A, Hämälä T, Young ND, Tiffin P. Combining GWAS and population genomic analyses to characterize coevolution in a legume-rhizobia symbiosis. Mol Ecol 2022. [PMID: 35793264 DOI: 10.1111/mec.16602] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Revised: 06/03/2022] [Accepted: 07/04/2022] [Indexed: 11/28/2022]
Abstract
The mutualism between legumes and rhizobia is clearly the product of past coevolution. However, the nature of ongoing evolution between these partners is less clear. To characterize the nature of recent coevolution between legumes and rhizobia, we used population genomic analysis to characterize selection on functionally annotated symbiosis genes as well as on symbiosis gene candidates identified through a two-species association analysis. For the association analysis, we inoculated each of 202 accessions of the legume host Medicago truncatula with a community of 88 Sinorhizobia (Ensifer) meliloti strains. Multistrain inoculation, which better reflects the ecological reality of rhizobial selection in nature than single-strain inoculation, allows strains to compete for nodulation opportunities and host resources and for hosts to preferentially form nodules and provide resources to some strains. We found extensive host by symbiont, that is, genotype-by-genotype, effects on rhizobial fitness and some annotated rhizobial genes bear signatures of recent positive selection. However, neither genes responsible for this variation nor annotated host symbiosis genes are enriched for signatures of either positive or balancing selection. This result suggests that stabilizing selection dominates selection acting on symbiotic traits and that variation in these traits is under mutation-selection balance. Consistent with the lack of positive selection acting on host genes, we found that among-host variation in growth was similar whether plants were grown with rhizobia or N-fertilizer, suggesting that the symbiosis may not be a major driver of variation in plant growth in multistrain contexts.
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Affiliation(s)
- Brendan Epstein
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - Liana T Burghardt
- Department of Plant Sciences, The University of Pennsylvania, University Park, Pennsylvania, USA
| | - Katy D Heath
- Department of Plant Biology, University of Illinois, Urbana, Illinois, USA.,Carl R. Woese Institute for Genomic Biology, University of Illinois, Urbana, Illinois, USA
| | - Michael A Grillo
- Department of Biology, Loyola University Chicago, Chicago, Illinois, USA
| | - Adam Kostanecki
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - Tuomas Hämälä
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA.,School of Life Sciences, University of Nottingham, Nottingham, UK
| | - Nevin D Young
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA.,Department of Plant Pathology, University of Minnesota, St. Paul, Minnesota, USA
| | - Peter Tiffin
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
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17
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Kitaeva AB, Gorshkov AP, Kusakin PG, Sadovskaya AR, Tsyganova AV, Tsyganov VE. Tubulin Cytoskeleton Organization in Cells of Determinate Nodules. FRONTIERS IN PLANT SCIENCE 2022; 13:823183. [PMID: 35557719 PMCID: PMC9087740 DOI: 10.3389/fpls.2022.823183] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/26/2021] [Accepted: 03/23/2022] [Indexed: 06/15/2023]
Abstract
Plant cell differentiation is based on rearrangements of the tubulin cytoskeleton; this is also true for symbiotic nodules. Nevertheless, although for indeterminate nodules (with a long-lasting meristem) the organization of microtubules during nodule development has been studied for various species, for determinate ones (with limited meristem activity) such studies are rare. Here, we investigated bacteroid morphology and dynamics of the tubulin cytoskeleton in determinate nodules of four legume species: Glycine max, Glycine soja, Phaseolus vulgaris, and Lotus japonicus. The most pronounced differentiation of bacteroids was observed in G. soja nodules. In meristematic cells in incipient nodules of all analyzed species, the organization of both cortical and endoplasmic microtubules was similar to that described for meristematic cells of indeterminate nodules. In young infected cells in developing nodules of all four species, cortical microtubules formed irregular patterns (microtubules were criss-crossed) and endoplasmic ones were associated with infection threads and infection droplets. Surprisingly, in uninfected cells the patterns of cortical microtubules differed in nodules of G. max and G. soja on the one hand, and P. vulgaris and L. japonicus on the other. The first two species exhibited irregular patterns, while the remaining two exhibited regular ones (microtubules were oriented transversely to the longitudinal axis of cell) that are typical for uninfected cells of indeterminate nodules. In contrast to indeterminate nodules, in mature determinate nodules of all four studied species, cortical microtubules formed a regular pattern in infected cells. Thus, our analysis revealed common patterns of tubulin cytoskeleton in the determinate nodules of four legume species, and species-specific differences were associated with the organization of cortical microtubules in uninfected cells. When compared with indeterminate nodules, the most pronounced differences were associated with the organization of cortical microtubules in nitrogen-fixing infected cells. The revealed differences indicated a possible transition during evolution of infected cells from anisotropic growth in determinate nodules to isodiametric growth in indeterminate nodules. It can be assumed that this transition provided an evolutionary advantage to those legume species with indeterminate nodules, enabling them to host symbiosomes in their infected cells more efficiently.
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Affiliation(s)
- Anna B. Kitaeva
- Laboratory of Molecular and Cellular Biology, All-Russia Research Institute for Agricultural Microbiology, Saint Petersburg, Russia
| | - Artemii P. Gorshkov
- Laboratory of Molecular and Cellular Biology, All-Russia Research Institute for Agricultural Microbiology, Saint Petersburg, Russia
| | - Pyotr G. Kusakin
- Laboratory of Molecular and Cellular Biology, All-Russia Research Institute for Agricultural Microbiology, Saint Petersburg, Russia
| | | | - Anna V. Tsyganova
- Laboratory of Molecular and Cellular Biology, All-Russia Research Institute for Agricultural Microbiology, Saint Petersburg, Russia
| | - Viktor E. Tsyganov
- Laboratory of Molecular and Cellular Biology, All-Russia Research Institute for Agricultural Microbiology, Saint Petersburg, Russia
- Saint Petersburg Scientific Center RAS, Saint Petersburg, Russia
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18
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Plant-Microbe Interaction in Sustainable Agriculture: The Factors That May Influence the Efficacy of PGPM Application. SUSTAINABILITY 2022. [DOI: 10.3390/su14042253] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The indiscriminate use of chemical fertilizers and pesticides has caused considerable environmental damage over the years. However, the growing demand for food in the coming years and decades requires the use of increasingly productive and efficient agriculture. Several studies carried out in recent years have shown how the application of plant growth-promoting microbes (PGPMs) can be a valid substitute for chemical industry products and represent a valid eco-friendly alternative. However, because of the complexity of interactions created with the numerous biotic and abiotic factors (i.e., environment, soil, interactions between microorganisms, etc.), the different formulates often show variable effects. In this review, we analyze the main factors that influence the effectiveness of PGPM applications and some of the applications that make them a useful tool for agroecological transition.
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19
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Wendlandt CE, Gano-Cohen KA, Stokes PJN, Jonnala BNR, Zomorrodian AJ, Al-Moussawi K, Sachs JL. Wild legumes maintain beneficial soil rhizobia populations despite decades of nitrogen deposition. Oecologia 2022; 198:419-430. [PMID: 35067801 DOI: 10.1007/s00442-022-05116-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Accepted: 01/10/2022] [Indexed: 10/19/2022]
Abstract
Natural landscapes are increasingly impacted by nitrogen enrichment from aquatic and airborne pollution sources. Nitrogen enrichment in the environment can eliminate the net benefits that plants gain from nitrogen-fixing microbes such as rhizobia, potentially altering host-mediated selection on nitrogen fixation. However, we know little about the long-term effects of nitrogen enrichment on this critical microbial service. Here, we sampled populations of the legume Acmispon strigosus and its associated soil microbial communities from sites spanning an anthropogenic nitrogen deposition gradient. We measured the net growth benefits plants obtained from their local soil microbial communities and quantified plant investment into nodules that house nitrogen-fixing rhizobia. We found that plant growth benefits from sympatric soil microbes did not vary in response to local soil nitrogen levels, and instead varied mainly among plant lines. Soil nitrogen levels positively predicted the number of nodules formed on sympatric plant hosts, although this was likely due to plant genotypic variation in nodule formation, rather than variation among soil microbial communities. The capacity of all the tested soil microbial communities to improve plant growth is consistent with plant populations imposing strong selection on rhizobial nitrogen fixation despite elevated soil nitrogen levels, suggesting that host control traits in A. strigosus are stable under long-term nutrient enrichment.
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Affiliation(s)
- Camille E Wendlandt
- Department of Botany and Plant Sciences, University of California, Riverside, CA, 92521, USA
| | - Kelsey A Gano-Cohen
- Department of Microbiology and Plant Pathology, University of California, Riverside, CA, 92521, USA
| | - Peter J N Stokes
- Department of Botany and Plant Sciences, University of California, Riverside, CA, 92521, USA
| | - Basava N R Jonnala
- Department of Evolution, Ecology and Organismal Biology, University of California, Riverside, CA, 92521, USA
| | - Avissa J Zomorrodian
- Department of Evolution, Ecology and Organismal Biology, University of California, Riverside, CA, 92521, USA
| | - Khadija Al-Moussawi
- Department of Evolution, Ecology and Organismal Biology, University of California, Riverside, CA, 92521, USA
| | - Joel L Sachs
- Department of Botany and Plant Sciences, University of California, Riverside, CA, 92521, USA. .,Department of Microbiology and Plant Pathology, University of California, Riverside, CA, 92521, USA. .,Department of Evolution, Ecology and Organismal Biology, University of California, Riverside, CA, 92521, USA.
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20
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Ortiz-Barbosa GS, Torres-Martínez L, Manci A, Neal S, Soubra T, Khairi F, Trinh J, Cardenas P, Sachs JL. No disruption of rhizobial symbiosis during early stages of cowpea domestication. Evolution 2022; 76:496-511. [PMID: 35014694 DOI: 10.1111/evo.14424] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 11/15/2021] [Accepted: 11/26/2021] [Indexed: 11/26/2022]
Abstract
Modern agriculture intensely selects aboveground plant structures, while often neglecting belowground features, and evolutionary tradeoffs between these traits are predicted to disrupt host control over microbiota. Moreover, drift, inbreeding, and relaxed selection for symbiosis in crops might degrade plant mechanisms that support beneficial microbes. We studied the impact of domestication on the nitrogen fixing symbiosis between cowpea and root-nodulating Bradyrhizobium. We combined genome-wide analyses with a greenhouse inoculation study to investigate genomic diversity, heritability, and symbiosis trait variation among wild and early-domesticated cowpea genotypes. Cowpeas experienced modest decreases in genome-wide diversity during early domestication. Nonetheless, domesticated cowpeas responded efficiently to variation in symbiotic effectiveness, by forming more root nodules with nitrogen-fixing rhizobia and sanctioning non-fixing strains. Domesticated populations invested a larger proportion of host tissues into root nodules than wild cowpeas. Unlike soybean and wheat, cowpea showed no compelling evidence for degradation of symbiosis during domestication. Domesticated cowpeas experienced a less severe bottleneck than these crops and the low nutrient conditions in Africa where cowpea landraces were developed likely favored plant genotypes that gain substantial benefits from symbiosis. Breeders have largely neglected symbiosis traits, but artificial selection for improved plant responses to microbiota could increase plant performance and sustainability. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- G S Ortiz-Barbosa
- Department of Microbiology & Plant Pathology, University of California, Riverside, CA
| | - L Torres-Martínez
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, CA
| | - A Manci
- Department of Microbiology & Plant Pathology, University of California, Riverside, CA
| | - S Neal
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, CA
| | - T Soubra
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, CA
| | - F Khairi
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, CA
| | - J Trinh
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, CA
| | - P Cardenas
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, CA
| | - J L Sachs
- Department of Microbiology & Plant Pathology, University of California, Riverside, CA.,Department of Evolution Ecology and Organismal Biology, University of California, Riverside, CA.,Institute of Integrative Genome Biology, University of California, Riverside, CA
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21
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Boivin S, Mahé F, Debellé F, Pervent M, Tancelin M, Tauzin M, Wielbo J, Mazurier S, Young P, Lepetit M. Genetic Variation in Host-Specific Competitiveness of the Symbiont Rhizobium leguminosarum Symbiovar viciae. FRONTIERS IN PLANT SCIENCE 2021; 12:719987. [PMID: 34567032 PMCID: PMC8457355 DOI: 10.3389/fpls.2021.719987] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Accepted: 07/29/2021] [Indexed: 05/25/2023]
Abstract
Legumes of the Fabeae tribe form nitrogen-fixing root nodules resulting from symbiotic interaction with the soil bacteria Rhizobium leguminosarum symbiovar viciae (Rlv). These bacteria are all potential symbionts of the Fabeae hosts but display variable partner choice when co-inoculated in mixture. Because partner choice and symbiotic nitrogen fixation mostly behave as genetically independent traits, the efficiency of symbiosis is often suboptimal when Fabeae legumes are exposed to natural Rlv populations present in soil. A core collection of 32 Rlv bacteria was constituted based on the genomic comparison of a collection of 121 genome sequences, representative of known worldwide diversity of Rlv. A variable part of the nodD gene sequence was used as a DNA barcode to discriminate and quantify each of the 32 bacteria in mixture. This core collection was co-inoculated on a panel of nine genetically diverse Pisum sativum, Vicia faba, and Lens culinaris genotypes. We estimated the relative Early Partner Choice (EPC) of the bacteria with the Fabeae hosts by DNA metabarcoding on the nodulated root systems. Comparative genomic analyses within the bacterial core collection identified molecular markers associated with host-dependent symbiotic partner choice. The results revealed emergent properties of rhizobial populations. They pave the way to identify genes related to important symbiotic traits operating at this level.
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Affiliation(s)
- Stéphane Boivin
- Laboratoire des Symbioses Tropicales et Méditerranéennes, INRAE, IRD, CIRAD, Montpellier SupAgro, University of Montpellier, Montpellier, France
| | - Frederic Mahé
- Biologie et Génétique des Interactions Plante-Parasite, CIRAD, INRAE, Montpellier SupAgro, University of Montpellier, Montpellier, France
| | - Frédéric Debellé
- Laboratoire des Interactions Plantes-Microorganismes, INRAE, CNRS, University of Toulouse, Castanet-Tolosan, France
| | - Marjorie Pervent
- Laboratoire des Symbioses Tropicales et Méditerranéennes, INRAE, IRD, CIRAD, Montpellier SupAgro, University of Montpellier, Montpellier, France
| | - Mathilde Tancelin
- Laboratoire des Symbioses Tropicales et Méditerranéennes, INRAE, IRD, CIRAD, Montpellier SupAgro, University of Montpellier, Montpellier, France
| | - Marc Tauzin
- Laboratoire des Symbioses Tropicales et Méditerranéennes, INRAE, IRD, CIRAD, Montpellier SupAgro, University of Montpellier, Montpellier, France
| | - Jerzy Wielbo
- Department of Genetics and Microbiology, Maria Curie-Skłodowska University, Lublin, Poland
| | - Sylvie Mazurier
- Agroecology, AgroSup Dijon, INRAE, University Burgundy Franche-Comté, Dijon, France
| | - Peter Young
- Department of Biology, University of York, York, United Kingdom
| | - Marc Lepetit
- Laboratoire des Symbioses Tropicales et Méditerranéennes, INRAE, IRD, CIRAD, Montpellier SupAgro, University of Montpellier, Montpellier, France
- Institut Sophia Agrobiotech, INRAE, CNRS, Côte d’Azur University, Sophia-Antipolis, France
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22
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Basile LA, Lepek VC. Legume-rhizobium dance: an agricultural tool that could be improved? Microb Biotechnol 2021; 14:1897-1917. [PMID: 34318611 PMCID: PMC8449669 DOI: 10.1111/1751-7915.13906] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Revised: 07/15/2021] [Accepted: 07/19/2021] [Indexed: 12/29/2022] Open
Abstract
The specific interaction between rhizobia and legume roots leads to the development of a highly regulated process called nodulation, by which the atmospheric nitrogen is converted into an assimilable plant nutrient. This capacity is the basis for the use of bacterial inoculants for field crop cultivation. Legume plants have acquired tools that allow the entry of compatible bacteria. Likewise, plants can impose sanctions against the maintenance of nodules occupied by rhizobia with low nitrogen-fixing capacity. At the same time, bacteria must overcome different obstacles posed first by the environment and then by the legume. The present review describes the mechanisms involved in the regulation of the entire legume-rhizobium symbiotic process and the strategies and tools of bacteria for reaching the nitrogen-fixing state inside the nodule. Also, we revised different approaches to improve the nodulation process for a better crop yield.
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Affiliation(s)
- Laura A. Basile
- Instituto de Investigaciones Biotecnológicas “Dr. Rodolfo A. Ugalde”Universidad Nacional de San Martín (IIB‐UNSAM‐CONICET)Av. 25 de Mayo y Francia, Gral. San Martín, Provincia de Buenos AiresBuenos AiresB1650HMPArgentina
| | - Viviana C. Lepek
- Instituto de Investigaciones Biotecnológicas “Dr. Rodolfo A. Ugalde”Universidad Nacional de San Martín (IIB‐UNSAM‐CONICET)Av. 25 de Mayo y Francia, Gral. San Martín, Provincia de Buenos AiresBuenos AiresB1650HMPArgentina
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23
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Mendoza-Suárez M, Andersen SU, Poole PS, Sánchez-Cañizares C. Competition, Nodule Occupancy, and Persistence of Inoculant Strains: Key Factors in the Rhizobium-Legume Symbioses. FRONTIERS IN PLANT SCIENCE 2021; 12:690567. [PMID: 34489993 PMCID: PMC8416774 DOI: 10.3389/fpls.2021.690567] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2021] [Accepted: 07/19/2021] [Indexed: 05/06/2023]
Abstract
Biological nitrogen fixation by Rhizobium-legume symbioses represents an environmentally friendly and inexpensive alternative to the use of chemical nitrogen fertilizers in legume crops. Rhizobial inoculants, applied frequently as biofertilizers, play an important role in sustainable agriculture. However, inoculants often fail to compete for nodule occupancy against native rhizobia with inferior nitrogen-fixing abilities, resulting in low yields. Strains with excellent performance under controlled conditions are typically selected as inoculants, but the rates of nodule occupancy compared to native strains are rarely investigated. Lack of persistence in the field after agricultural cycles, usually due to the transfer of symbiotic genes from the inoculant strain to naturalized populations, also limits the suitability of commercial inoculants. When rhizobial inoculants are based on native strains with a high nitrogen fixation ability, they often have superior performance in the field due to their genetic adaptations to the local environment. Therefore, knowledge from laboratory studies assessing competition and understanding how diverse strains of rhizobia behave, together with assays done under field conditions, may allow us to exploit the effectiveness of native populations selected as elite strains and to breed specific host cultivar-rhizobial strain combinations. Here, we review current knowledge at the molecular level on competition for nodulation and the advances in molecular tools for assessing competitiveness. We then describe ongoing approaches for inoculant development based on native strains and emphasize future perspectives and applications using a multidisciplinary approach to ensure optimal performance of both symbiotic partners.
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Affiliation(s)
| | - Stig U. Andersen
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Philip S. Poole
- Department of Plant Sciences, University of Oxford, Oxford, United Kingdom
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24
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Denison RF. Legume-imposed selection for more-efficient symbiotic rhizobia. Proc Natl Acad Sci U S A 2021; 118:e2107033118. [PMID: 33972460 PMCID: PMC8179168 DOI: 10.1073/pnas.2107033118] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Affiliation(s)
- R Ford Denison
- Department of Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, MN 55108
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25
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Quides KW, Weisberg AJ, Trinh J, Salaheldine F, Cardenas P, Lee HH, Jariwala R, Chang JH, Sachs JL. Experimental evolution can enhance benefits of rhizobia to novel legume hosts. Proc Biol Sci 2021; 288:20210812. [PMID: 34034525 PMCID: PMC8150021 DOI: 10.1098/rspb.2021.0812] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Legumes preferentially associate with and reward beneficial rhizobia in root nodules, but the processes by which rhizobia evolve to provide benefits to novel hosts remain poorly understood. Using cycles of in planta and in vitro evolution, we experimentally simulated lifestyles where rhizobia repeatedly interact with novel plant genotypes with which they initially provide negligible benefits. Using a full-factorial replicated design, we independently evolved two rhizobia strains in associations with each of two Lotus japonicus genotypes that vary in regulation of nodule formation. We evaluated phenotypic evolution of rhizobia by quantifying fitness, growth effects and histological features on hosts, and molecular evolution via genome resequencing. Rhizobia evolved enhanced host benefits and caused changes in nodule development in one of the four host–symbiont combinations, that appeared to be driven by reduced costs during symbiosis, rather than increased nitrogen fixation. Descendant populations included genetic changes that could alter rhizobial infection or proliferation in host tissues, but lack of evidence for fixation of these mutations weakens the results. Evolution of enhanced rhizobial benefits occurred only in a subset of experiments, suggesting a role for host–symbiont genotype interactions in mediating the evolution of enhanced benefits from symbionts.
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Affiliation(s)
- Kenjiro W Quides
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, USA
| | - Alexandra J Weisberg
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, USA
| | - Jerry Trinh
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, USA
| | - Fathi Salaheldine
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, USA
| | - Paola Cardenas
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, USA
| | - Hsu-Han Lee
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, USA
| | - Ruchi Jariwala
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, USA
| | - Jeff H Chang
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, USA
| | - Joel L Sachs
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, USA.,Department of Microbiology and Plant Pathology, University of California, Riverside, CA, USA.,Institute for Integrative Genome Biology, University of California, Riverside, CA, USA
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26
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Westhoek A, Clark LJ, Culbert M, Dalchau N, Griffiths M, Jorrin B, Karunakaran R, Ledermann R, Tkacz A, Webb I, James EK, Poole PS, Turnbull LA. Conditional sanctioning in a legume- Rhizobium mutualism. Proc Natl Acad Sci U S A 2021; 118:e2025760118. [PMID: 33941672 PMCID: PMC8126861 DOI: 10.1073/pnas.2025760118] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Legumes are high in protein and form a valuable part of human diets due to their interaction with symbiotic nitrogen-fixing bacteria known as rhizobia. Plants house rhizobia in specialized root nodules and provide the rhizobia with carbon in return for nitrogen. However, plants usually house multiple rhizobial strains that vary in their fixation ability, so the plant faces an investment dilemma. Plants are known to sanction strains that do not fix nitrogen, but nonfixers are rare in field settings, while intermediate fixers are common. Here, we modeled how plants should respond to an intermediate fixer that was otherwise isogenic and tested model predictions using pea plants. Intermediate fixers were only tolerated when a better strain was not available. In agreement with model predictions, nodules containing the intermediate-fixing strain were large and healthy when the only alternative was a nonfixer, but nodules of the intermediate-fixing strain were small and white when the plant was coinoculated with a more effective strain. The reduction in nodule size was preceded by a lower carbon supply to the nodule even before differences in nodule size could be observed. Sanctioned nodules had reduced rates of nitrogen fixation, and in later developmental stages, sanctioned nodules contained fewer viable bacteria than nonsanctioned nodules. This indicates that legumes can make conditional decisions, most likely by comparing a local nodule-dependent cue of nitrogen output with a global cue, giving them remarkable control over their symbiotic partners.
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Affiliation(s)
- Annet Westhoek
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
- Systems Biology Doctoral Training Centre, Doctoral Training Centre, University of Oxford, OX1 3NP Oxford, United Kingdom
| | - Laura J Clark
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
| | - Michael Culbert
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
| | - Neil Dalchau
- Biological Computation, Microsoft Research Cambridge, CB1 2FB Cambridge, United Kingdom
| | - Megan Griffiths
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
| | - Beatriz Jorrin
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
| | - Ramakrishnan Karunakaran
- Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, NR4 7UH Norwich, United Kingdom
| | - Raphael Ledermann
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
| | - Andrzej Tkacz
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
| | - Isabel Webb
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
| | - Euan K James
- Ecological Sciences, The James Hutton Institute, DD2 5DA Invergowrie, United Kingdom
| | - Philip S Poole
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom;
| | - Lindsay A Turnbull
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom;
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27
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Torres-Martínez L, Porter SS, Wendlandt C, Purcell J, Ortiz-Barbosa G, Rothschild J, Lampe M, Warisha F, Le T, Weisberg AJ, Chang JH, Sachs JL. Evolution of specialization in a plant-microbial mutualism is explained by the oscillation theory of speciation. Evolution 2021; 75:1070-1086. [PMID: 33782951 DOI: 10.1111/evo.14222] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Revised: 02/18/2021] [Accepted: 03/14/2021] [Indexed: 12/11/2022]
Abstract
Specialization in mutualisms is thought to be a major driver of diversification, but few studies have explored how novel specialization evolves, or its relation to the evolution of other niche axes. A fundamental question is whether generalist interactions evolve to become more specialized (i.e., oscillation hypothesis) or if partner switches evolve without any change in niche breadth (i.e., musical chairs hypothesis). We examined alternative models for the evolution of specialization by estimating the mutualistic, climatic, and edaphic niche breadths of sister plant species, combining phylogenetic, environmental, and experimental data on Acmispon strigosus and Acmispon wrangelianus genotypes across their overlapping ranges in California. We found that specialization along all three niche axes was asymmetric across species, such that the species with broader climatic and edaphic niches, Acmispon strigosus, was also able to gain benefit from and invest in associating with a broader set of microbial mutualists. Our data are consistent with the oscillation model of specialization, and a parallel narrowing of the edaphic, climatic, and mutualistic dimensions of the host species niche. Our findings provide novel evidence that the evolution of specialization in mutualism is accompanied by specialization in other niche dimensions.
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Affiliation(s)
- Lorena Torres-Martínez
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, California, 92521
| | - Stephanie S Porter
- School of Biological Sciences, Washington State University, Vancouver, Washington, 98686, United States of America
| | - Camille Wendlandt
- School of Biological Sciences, Washington State University, Vancouver, Washington, 98686, United States of America
| | - Jessica Purcell
- Department of Entomology, University of California, Riverside, California, 92521, United States of America
| | - Gabriel Ortiz-Barbosa
- Department of Microbiology and Plant Pathology, University of California, Riverside, California, 92521, United States of America
| | - Jacob Rothschild
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, California, 92521
| | - Mathew Lampe
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, California, 92521
| | - Farsamin Warisha
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, California, 92521
| | - Tram Le
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, California, 92521
| | - Alexandra J Weisberg
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, 97331, United States of America
| | - Jeff H Chang
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, 97331, United States of America
| | - Joel L Sachs
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, California, 92521.,Department of Microbiology and Plant Pathology, University of California, Riverside, California, 92521, United States of America.,Institute of Integrative Genome Biology, University of California, Riverside, California, 92521, United States of America
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28
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Quides KW, Salaheldine F, Jariwala R, Sachs JL. Dysregulation of host-control causes interspecific conflict over host investment into symbiotic organs. Evolution 2021; 75:1189-1200. [PMID: 33521949 DOI: 10.1111/evo.14173] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 10/31/2020] [Accepted: 01/08/2021] [Indexed: 12/14/2022]
Abstract
Microbial mutualists provide substantial benefits to hosts that feed back to enhance the fitness of the associated microbes. In many systems, beneficial microbes colonize symbiotic organs, specialized host structures that house symbionts and mediate resources exchanged between parties. Mutualisms are characterized by net benefits exchanged among members of different species, however, inequalities in the magnitude of these exchanges could result in evolutionary conflict, destabilizing the mutualism. We investigated joint fitness effects of root nodule formation, the symbiotic organ of legumes that house nitrogen-fixing rhizobia in planta. We quantified host and symbiont fitness parameters dependent on the number of nodules formed using near-isogenic Lotus japonicus and Mesorhizobium loti mutants, respectively. Empirically estimated fitness functions suggest that legume and rhizobia fitness is aligned as the number of nodules formed increases from zero until the host optimum is reached, a point where aligned fitness interests shift to diverging fitness interests between host and symbiont. However, fitness conflict was only inferred when analyzing wild-type hosts along with their mutants dysregulated for control over nodule formation. These data demonstrate that to avoid conflict, hosts must tightly regulate investment into symbiotic organs maximizing their benefit to cost ratio of associating with microbes.
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Affiliation(s)
- Kenjiro W Quides
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, California, 92521, USA.,Current Institution: Schmid College of Science and Technology, Chapman University, Orange, California, USA
| | - Fathi Salaheldine
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, California, 92521, USA
| | - Ruchi Jariwala
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, California, 92521, USA
| | - Joel L Sachs
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, California, 92521, USA.,Institute for Integrative Genome Biology, University of California, Riverside, California, USA
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29
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Abstract
Rhizobia are a phylogenetically diverse group of soil bacteria that engage in mutualistic interactions with legume plants. Although specifics of the symbioses differ between strains and plants, all symbioses ultimately result in the formation of specialized root nodule organs which host the nitrogen-fixing microsymbionts called bacteroids. Inside nodules, bacteroids encounter unique conditions that necessitate global reprogramming of physiological processes and rerouting of their metabolism. Decades of research have addressed these questions using genetics, omics approaches, and more recently computational modelling. Here we discuss the common adaptations of rhizobia to the nodule environment that define the core principles of bacteroid functioning. All bacteroids are growth-arrested and perform energy-intensive nitrogen fixation fueled by plant-provided C4-dicarboxylates at nanomolar oxygen levels. At the same time, bacteroids are subject to host control and sanctioning that ultimately determine their fitness and have fundamental importance for the evolution of a stable mutualistic relationship.
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30
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Vaidya P, Stinchcombe JR. The Potential for Genotype-by-Environment Interactions to Maintain Genetic Variation in a Model Legume-Rhizobia Mutualism. PLANT COMMUNICATIONS 2020; 1:100114. [PMID: 33367267 PMCID: PMC7747969 DOI: 10.1016/j.xplc.2020.100114] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 09/10/2020] [Accepted: 10/08/2020] [Indexed: 05/10/2023]
Abstract
The maintenance of genetic variation in mutualism-related traits is key for understanding mutualism evolution, yet the mechanisms maintaining variation remain unclear. We asked whether genotype-by-environment (G×E) interaction is a potential mechanism maintaining variation in the model legume-rhizobia system, Medicago truncatula-Ensifer meliloti. We planted 50 legume genotypes in a greenhouse under ambient light and shade to reflect reduced carbon availability for plants. We found an expected reduction under shaded conditions for plant performance traits, such as leaf number, aboveground and belowground biomass, and a mutualism-related trait, nodule number. We also found G×E for nodule number, with ∼83% of this interaction due to shifts in genotype fitness rank order across light environments, coupled with strong positive directional selection on nodule number regardless of light environment. Our results suggest that G×E can maintain genetic variation in a mutualism-related trait that is under consistent positive directional selection across light environments.
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Affiliation(s)
- Priya Vaidya
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON M5S3B2, Canada
- Corresponding author
| | - John R. Stinchcombe
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON M5S3B2, Canada
- Koffler Scientific Reserve at Joker's Hill, University of Toronto, Toronto, ON M5S3B2, Canada
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31
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Chomicki G, Kiers ET, Renner SS. The Evolution of Mutualistic Dependence. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2020. [DOI: 10.1146/annurev-ecolsys-110218-024629] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
While the importance of mutualisms across the tree of life is recognized, it is not understood why some organisms evolve high levels of dependence on mutualistic partnerships, while other species remain autonomous or retain or regain minimal dependence on partners. We identify four main pathways leading to the evolution of mutualistic dependence. Then, we evaluate current evidence for three predictions: ( a) Mutualisms with different levels of dependence have distinct stabilizing mechanisms against exploitation and cheating, ( b) less dependent mutualists will return to autonomy more often than those that are highly dependent, and ( c) obligate mutualisms should be less context dependent than facultative ones. Although we find evidence supporting all three predictions, we stress that mutualistic partners follow diverse paths toward—and away from—dependence. We also highlight the need to better examine asymmetry in partner dependence. Recognizing how variation in dependence influences the stability, breakdown, and context dependence of mutualisms generates new hypotheses regarding how and why the benefits of mutualistic partnerships differ over time and space.
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Affiliation(s)
- Guillaume Chomicki
- Department of Bioscience, Durham University, Durham DH1 3LE, United Kingdom
| | - E. Toby Kiers
- Department of Ecological Science, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands
| | - Susanne S. Renner
- Systematic Botany and Mycology, Department of Biology, University of Munich (LMU), 80638 Munich, Germany
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32
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Chomicki G, Werner GDA, West SA, Kiers ET. Compartmentalization drives the evolution of symbiotic cooperation. Philos Trans R Soc Lond B Biol Sci 2020; 375:20190602. [PMID: 32772665 DOI: 10.1098/rstb.2019.0602] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Across the tree of life, hosts have evolved mechanisms to control and mediate interactions with symbiotic partners. We suggest that the evolution of physical structures that allow hosts to spatially separate symbionts, termed compartmentalization, is a common mechanism used by hosts. Such compartmentalization allows hosts to: (i) isolate symbionts and control their reproduction; (ii) reward cooperative symbionts and punish or stop interactions with non-cooperative symbionts; and (iii) reduce direct conflict among different symbionts strains in a single host. Compartmentalization has allowed hosts to increase the benefits that they obtain from symbiotic partners across a diversity of interactions, including legumes and rhizobia, plants and fungi, squid and Vibrio, insects and nutrient provisioning bacteria, plants and insects, and the human microbiome. In cases where compartmentalization has not evolved, we ask why not. We argue that when partners interact in a competitive hierarchy, or when hosts engage in partnerships which are less costly, compartmentalization is less likely to evolve. We conclude that compartmentalization is key to understanding the evolution of symbiotic cooperation. This article is part of the theme issue 'The role of the microbiome in host evolution'.
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Affiliation(s)
- Guillaume Chomicki
- Department of Biosciences, Durham University, Stockton Road, Durham DH1 3LE, UK
| | - Gijsbert D A Werner
- Department of Zoology, University of Oxford, Zoology Research and Administration Building, 11a Mansfield Road, Oxford OX1 3SZ, UK.,Netherlands Scientific Council for Government Policy, Buitenhof 34, 2513 AH Den Haag, The Netherlands
| | - Stuart A West
- Department of Zoology, University of Oxford, Zoology Research and Administration Building, 11a Mansfield Road, Oxford OX1 3SZ, UK
| | - E Toby Kiers
- Department of Ecological Science, VU University, Amsterdam, The Netherlands
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33
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Agtuca BJ, Stopka SA, Evans S, Samarah L, Liu Y, Xu D, Stacey MG, Koppenaal DW, Paša-Tolić L, Anderton CR, Vertes A, Stacey G. Metabolomic profiling of wild-type and mutant soybean root nodules using laser-ablation electrospray ionization mass spectrometry reveals altered metabolism. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2020; 103:1937-1958. [PMID: 32410239 DOI: 10.1111/tpj.14815] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Revised: 04/05/2020] [Accepted: 04/17/2020] [Indexed: 05/18/2023]
Abstract
The establishment of the nitrogen-fixing symbiosis between soybean and Bradyrhizobium japonicum is a complex process. To document the changes in plant metabolism as a result of symbiosis, we utilized laser ablation electrospray ionization-mass spectrometry (LAESI-MS) for in situ metabolic profiling of wild-type nodules, nodules infected with a B. japonicum nifH mutant unable to fix nitrogen, nodules doubly infected by both strains, and nodules formed on plants mutated in the stearoyl-acyl carrier protein desaturase (sacpd-c) gene, which were previously shown to have an altered nodule ultrastructure. The results showed that the relative abundance of fatty acids, purines, and lipids was significantly changed in response to the symbiosis. The nifH mutant nodules had elevated levels of jasmonic acid, correlating with signs of nitrogen deprivation. Nodules resulting from the mixed inoculant displayed similar, overlapping metabolic distributions within the sectors of effective (fix+ ) and ineffective (nifH mutant, fix- ) endosymbionts. These data are inconsistent with the notion that plant sanctioning is cell autonomous. Nodules lacking sacpd-c displayed an elevation of soyasaponins and organic acids in the central necrotic regions. The present study demonstrates the utility of LAESI-MS for high-throughput screening of plant phenotypes. Overall, nodules disrupted in the symbiosis were elevated in metabolites related to plant defense.
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Affiliation(s)
- Beverly J Agtuca
- Divisions of Plant Sciences and Biochemistry, Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA
| | - Sylwia A Stopka
- Department of Chemistry, The George Washington University, Washington, DC, 20052, USA
| | - Sterling Evans
- Divisions of Plant Sciences and Biochemistry, Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA
| | - Laith Samarah
- Department of Chemistry, The George Washington University, Washington, DC, 20052, USA
| | - Yang Liu
- Department of Electrical Engineering and Computer Science, Informatics Institute and Christopher S. Bond Life Sciences Center, University of Missouri-Columbia, Columbia, MO, 65211, USA
| | - Dong Xu
- Department of Electrical Engineering and Computer Science, Informatics Institute and Christopher S. Bond Life Sciences Center, University of Missouri-Columbia, Columbia, MO, 65211, USA
| | - Minviluz G Stacey
- Divisions of Plant Sciences and Biochemistry, Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA
| | - David W Koppenaal
- Environmental Molecular Sciences Laboratory, Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, WA, 99354, USA
| | - Ljiljana Paša-Tolić
- Environmental Molecular Sciences Laboratory, Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, WA, 99354, USA
| | - Christopher R Anderton
- Environmental Molecular Sciences Laboratory, Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, WA, 99354, USA
| | - Akos Vertes
- Department of Chemistry, The George Washington University, Washington, DC, 20052, USA
| | - Gary Stacey
- Divisions of Plant Sciences and Biochemistry, Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA
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34
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Younginger BS, Friesen ML. Connecting signals and benefits through partner choice in plant-microbe interactions. FEMS Microbiol Lett 2020; 366:5626345. [PMID: 31730203 DOI: 10.1093/femsle/fnz217] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2018] [Accepted: 10/17/2019] [Indexed: 12/20/2022] Open
Abstract
Stabilizing mechanisms in plant-microbe symbioses are critical to maintaining beneficial functions, with two main classes: host sanctions and partner choice. Sanctions are currently presumed to be more effective and widespread, based on the idea that microbes rapidly evolve cheating while retaining signals matching cooperative strains. However, hosts that effectively discriminate among a pool of compatible symbionts would gain a significant fitness advantage. Using the well-characterized legume-rhizobium symbiosis as a model, we evaluate the evidence for partner choice in the context of the growing field of genomics. Empirical studies that rely upon bacteria varying only in nitrogen-fixation ability ignore host-symbiont signaling and frequently conclude that partner choice is not a robust stabilizing mechanism. Here, we argue that partner choice is an overlooked mechanism of mutualism stability and emphasize that plants need not use the microbial services provided a priori to discriminate among suitable partners. Additionally, we present a model that shows that partner choice signaling increases symbiont and host fitness in the absence of sanctions. Finally, we call for a renewed focus on elucidating the signaling mechanisms that are critical to partner choice while further aiming to understand their evolutionary dynamics in nature.
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Affiliation(s)
- Brett S Younginger
- Department of Plant Pathology, Washington State University, PO Box 646430, 345 Johnson Hall, Pullman, WA 99164, USA
| | - Maren L Friesen
- Department of Plant Pathology, Washington State University, PO Box 646430, 345 Johnson Hall, Pullman, WA 99164, USA.,Department of Crop and Soil Sciences, Washington State University, PO Box 646420, 115 Johnson Hall, Pullman, WA 99164, USA
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Mendoza-Suárez MA, Geddes BA, Sánchez-Cañizares C, Ramírez-González RH, Kirchhelle C, Jorrin B, Poole PS. Optimizing Rhizobium-legume symbioses by simultaneous measurement of rhizobial competitiveness and N 2 fixation in nodules. Proc Natl Acad Sci U S A 2020; 117:9822-9831. [PMID: 32317381 PMCID: PMC7211974 DOI: 10.1073/pnas.1921225117] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Legumes tend to be nodulated by competitive rhizobia that do not maximize nitrogen (N2) fixation, resulting in suboptimal yields. Rhizobial nodulation competitiveness and effectiveness at N2 fixation are independent traits, making their measurement extremely time-consuming with low experimental throughput. To transform the experimental assessment of rhizobial competitiveness and effectiveness, we have used synthetic biology to develop reporter plasmids that allow simultaneous high-throughput measurement of N2 fixation in individual nodules using green fluorescent protein (GFP) and barcode strain identification (Plasmid ID) through next generation sequencing (NGS). In a proof-of-concept experiment using this technology in an agricultural soil, we simultaneously monitored 84 different Rhizobium leguminosarum strains, identifying a supercompetitive and highly effective rhizobial symbiont for peas. We also observed a remarkable frequency of nodule coinfection by rhizobia, with mixed occupancy identified in ∼20% of nodules, containing up to six different strains. Critically, this process can be adapted to multiple Rhizobium-legume symbioses, soil types, and environmental conditions to permit easy identification of optimal rhizobial inoculants for field testing to maximize agricultural yield.
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Affiliation(s)
| | - Barney A Geddes
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
| | | | | | - Charlotte Kirchhelle
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
| | - Beatriz Jorrin
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom
| | - Philip S Poole
- Department of Plant Sciences, University of Oxford, OX1 3RB Oxford, United Kingdom;
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Doin de Moura GG, Remigi P, Masson-Boivin C, Capela D. Experimental Evolution of Legume Symbionts: What Have We Learnt? Genes (Basel) 2020; 11:E339. [PMID: 32210028 PMCID: PMC7141107 DOI: 10.3390/genes11030339] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Revised: 03/17/2020] [Accepted: 03/20/2020] [Indexed: 12/11/2022] Open
Abstract
Rhizobia, the nitrogen-fixing symbionts of legumes, are polyphyletic bacteria distributed in many alpha- and beta-proteobacterial genera. They likely emerged and diversified through independent horizontal transfers of key symbiotic genes. To replay the evolution of a new rhizobium genus under laboratory conditions, the symbiotic plasmid of Cupriavidus taiwanensis was introduced in the plant pathogen Ralstonia solanacearum, and the generated proto-rhizobium was submitted to repeated inoculations to the C. taiwanensis host, Mimosa pudica L.. This experiment validated a two-step evolutionary scenario of key symbiotic gene acquisition followed by genome remodeling under plant selection. Nodulation and nodule cell infection were obtained and optimized mainly via the rewiring of regulatory circuits of the recipient bacterium. Symbiotic adaptation was shown to be accelerated by the activity of a mutagenesis cassette conserved in most rhizobia. Investigating mutated genes led us to identify new components of R. solanacearum virulence and C. taiwanensis symbiosis. Nitrogen fixation was not acquired in our short experiment. However, we showed that post-infection sanctions allowed the increase in frequency of nitrogen-fixing variants among a non-fixing population in the M. pudica-C. taiwanensis system and likely allowed the spread of this trait in natura. Experimental evolution thus provided new insights into rhizobium biology and evolution.
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Affiliation(s)
| | | | | | - Delphine Capela
- LIPM, Université de Toulouse, INRAE, CNRS, Castanet-Tolosan 31320, France; (G.G.D.d.M.); (P.R.); (C.M.-B.)
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Dupin SE, Geurts R, Kiers ET. The Non-Legume Parasponia andersonii Mediates the Fitness of Nitrogen-Fixing Rhizobial Symbionts Under High Nitrogen Conditions. FRONTIERS IN PLANT SCIENCE 2020; 10:1779. [PMID: 32117343 PMCID: PMC7019102 DOI: 10.3389/fpls.2019.01779] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Accepted: 12/20/2019] [Indexed: 05/13/2023]
Abstract
Organisms rely on symbiotic associations for metabolism, protection, and energy. However, these intimate partnerships can be vulnerable to exploitation. What prevents microbial mutualists from parasitizing their hosts? In legumes, there is evidence that hosts have evolved sophisticated mechanisms to manage their symbiotic rhizobia, but the generality and evolutionary origins of these control mechanisms are under debate. Here, we focused on the symbiosis between Parasponia hosts and N2-fixing rhizobium bacteria. Parasponia is the only non-legume lineage to have evolved a rhizobial symbiosis and thus provides an evolutionary replicate to test how rhizobial exploitation is controlled. A key question is whether Parasponia hosts can prevent colonization of rhizobia under high nitrogen conditions, when the contribution of the symbiont becomes nonessential. We grew Parasponia andersonii inoculated with Bradyrhizobium elkanii under four ammonium nitrate concentrations in a controlled growth chamber. We measured shoot and root dry weight, nodule number, nodule fresh weight, nodule volume. To quantify viable rhizobial populations in planta, we crushed nodules and determined colony forming units (CFU), as a rhizobia fitness proxy. We show that, like legumes and actinorhizal plants, P. andersonii is able to control nodule symbiosis in response to exogenous nitrogen. While the relative host growth benefits of inoculation decreased with nitrogen fertilization, our highest ammonium nitrate concentration (3.75 mM) was sufficient to prevent nodule formation on inoculated roots. Rhizobial populations were highest in nitrogen free medium. While we do not yet know the mechanism, our results suggest that control mechanisms over rhizobia are not exclusive to the legume clade.
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Affiliation(s)
- Simon E. Dupin
- Department of Ecological Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
- Department of Plant Sciences, Wageningen University, Wageningen, Netherlands
| | - René Geurts
- Department of Plant Sciences, Wageningen University, Wageningen, Netherlands
| | - E. Toby Kiers
- Department of Ecological Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
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Forrester NJ, Ashman TL. Autopolyploidy alters nodule-level interactions in the legume-rhizobium mutualism. AMERICAN JOURNAL OF BOTANY 2020; 107:179-185. [PMID: 31721161 DOI: 10.1002/ajb2.1375] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2019] [Accepted: 06/17/2019] [Indexed: 05/22/2023]
Abstract
PREMISE Polyploidy is a major genetic driver of ecological and evolutionary processes in plants, yet its effects on plant interactions with mutualistic microbes remain unresolved. The legume-rhizobium symbiosis regulates global nutrient cycles and plays a role in the diversification of legume species. In this mutualism, rhizobia bacteria fix nitrogen in exchange for carbon provided by legume hosts. This exchange occurs inside root nodules, which house bacterial cells and represent the interface of legume-rhizobium interactions. Although polyploidy may directly impact the legume-rhizobium mutualism, no studies have explored how it alters the internal structure of nodules. METHODS We created synthetic autotetraploids using Medicago sativa subsp. caerulea. Neotetraploid plants and their diploid progenitors were singly inoculated with two strains of rhizobia, Sinorhizobium meliloti and S. medicae. Confocal microscopy was used to quantify internal traits of nodules produced by diploid and neotetraploid plants. RESULTS Autotetraploid plants produced larger nodules with larger nitrogen fixation zones than diploids for both strains of rhizobia, although the significance of these differences was limited by power. Neotetraploid M. sativa subsp. caerulea plants also produced symbiosomes that were significantly larger, nearly twice the size, than those present in diploids. CONCLUSIONS This study sheds light on how polyploidy directly affects a plant-bacterium mutualism and uncovers novel mechanisms. Changes in plant-microbe interactions that directly result from polyploidy likely contribute to the increased ability of polyploid legumes to establish in diverse environments.
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Affiliation(s)
- Nicole J Forrester
- Department of Biological Sciences, University of Pittsburgh, 4249 Fifth Avenue, Pittsburgh, PA, 15260, USA
| | - Tia-Lynn Ashman
- Department of Biological Sciences, University of Pittsburgh, 4249 Fifth Avenue, Pittsburgh, PA, 15260, USA
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Gano-Cohen KA, Wendlandt CE, Al Moussawi K, Stokes PJ, Quides KW, Weisberg AJ, Chang JH, Sachs JL. Recurrent mutualism breakdown events in a legume rhizobia metapopulation. Proc Biol Sci 2020; 287:20192549. [PMID: 31992172 DOI: 10.1098/rspb.2019.2549] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Bacterial mutualists generate major fitness benefits for eukaryotes, reshaping the host phenotype and its interactions with the environment. Yet, microbial mutualist populations are predicted to generate mutants that defect from providing costly services to hosts while maintaining the capacity to exploit host resources. Here, we examined the mutualist service of symbiotic nitrogen fixation in a metapopulation of root-nodulating Bradyrhizobium spp. that associate with the native legume Acmispon strigosus. We quantified mutualism traits of 85 Bradyrhizobium isolates gathered from a 700 km transect in California spanning 10 sampled A. strigosus populations. We clonally inoculated each Bradyrhizobium isolate onto A. strigosus hosts and quantified nodulation capacity and net effects of infection, including host growth and isotopic nitrogen concentration. Six Bradyrhizobium isolates from five populations were categorized as ineffective because they formed nodules but did not enhance host growth via nitrogen fixation. Six additional isolates from three populations failed to form root nodules. Phylogenetic reconstruction inferred two types of mutualism breakdown, including three to four independent losses of effectiveness and five losses of nodulation capacity on A. strigosus. The evolutionary and genomic drivers of these mutualism breakdown events remain poorly understood.
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Affiliation(s)
- Kelsey A Gano-Cohen
- Department of Microbiology and Plant Pathology, University of California, Riverside, CA, USA
| | - Camille E Wendlandt
- Department of Botany and Plant Sciences, University of California, Riverside, CA, USA
| | - Khadija Al Moussawi
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, CA, USA
| | - Peter J Stokes
- Department of Botany and Plant Sciences, University of California, Riverside, CA, USA
| | - Kenjiro W Quides
- Department of Evolution Ecology and Organismal Biology, University of California, Riverside, CA, USA
| | - Alexandra J Weisberg
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, USA
| | - Jeff H Chang
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, USA
| | - Joel L Sachs
- Department of Microbiology and Plant Pathology, University of California, Riverside, CA, USA.,Department of Botany and Plant Sciences, University of California, Riverside, CA, USA.,Department of Evolution Ecology and Organismal Biology, University of California, Riverside, CA, USA.,Institute for Integrative Genome Biology, University of California, Riverside, CA, USA
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Favero VO, Carvalho RH, Motta VM, Leite ABC, Coelho MRR, Xavier GR, Rumjanek NG, Urquiaga S. Bradyrhizobium as the Only Rhizobial Inhabitant of Mung Bean ( Vigna radiata) Nodules in Tropical Soils: A Strategy Based on Microbiome for Improving Biological Nitrogen Fixation Using Bio-Products. FRONTIERS IN PLANT SCIENCE 2020; 11:602645. [PMID: 33510747 PMCID: PMC7835340 DOI: 10.3389/fpls.2020.602645] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 12/14/2020] [Indexed: 05/07/2023]
Abstract
The mung bean has a great potential under tropical conditions given its high content of grain protein. Additionally, its ability to benefit from biological nitrogen fixation (BNF) through association with native rhizobia inhabiting nodule microbiome provides most of the nitrogen independence on fertilizers. Soil microbial communities which are influenced by biogeographical factors and soil properties, represent a source of rhizobacteria capable of stimulating plant growth. The objective of this study is to support selection of beneficial bacteria that form positive interactions with mung bean plants cultivated in tropical soils, as part of a seed inoculation program for increasing grain yield based on the BNF and other mechanisms. Two mung bean genotypes (Camaleão and Esmeralda) were cultivated in 10 soil samples. Nodule microbiome was characterized by next-generation sequencing using Illumina MiSeq 16S rRNA. More than 99% of nodule sequences showed similarity with Bradyrhizobium genus, the only rhizobial present in nodules in our study. Higher bacterial diversity of soil samples collected in agribusiness areas (MW_MT-I, II or III) was associated with Esmeralda genotype, while an organic agroecosystem soil sample (SE_RJ-V) showed the highest bacterial diversity independent of genotype. Furthermore, OTUs close to Bradyrhizobium elkanii have dominated in all soil samples, except in the sample from the organic agroecosystem, where just B. japonicum was present. Bacterial community of mung bean nodules is mainly influenced by soil pH, K, Ca, and P. Besides a difference on nodule colonization by OTU sequences close to the Pseudomonas genus regarding the two genotypes was detected too. Although representing a small rate, around 0.1% of the total, Pseudomonas OTUs were only retrieved from nodules of Esmeralda genotype, suggesting a different trait regarding specificity between macro- and micro-symbionts. The microbiome analysis will guide the next steps in the development of an inoculant for mung bean aiming to promote plant growth and grain yield, composed either by an efficient Bradyrhizobium strain on its own or co-inoculated with a Pseudomonas strain. Considering the results achieved, the assessment of microbial ecology parameters is a potent coadjuvant capable to accelerate the inoculant development process and to improve the benefits to the crop by soil microorganisms.
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Affiliation(s)
| | | | | | | | | | | | - Norma Gouvêa Rumjanek
- Embrapa Agrobiology, Seropédica, Rio de Janeiro, Brazil
- *Correspondence: Norma Gouvêa Rumjanek,
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Gunnabo AH, Geurts R, Wolde-Meskel E, Degefu T, Giller KE, van Heerwaarden J. Genetic Interaction Studies Reveal Superior Performance of Rhizobium tropici CIAT899 on a Range of Diverse East African Common Bean (Phaseolus vulgaris L.) Genotypes. Appl Environ Microbiol 2019; 85:e01763-19. [PMID: 31562174 PMCID: PMC6881787 DOI: 10.1128/aem.01763-19] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Accepted: 09/25/2019] [Indexed: 02/07/2023] Open
Abstract
We studied symbiotic performance of factorial combinations of diverse rhizobial genotypes (GR) and East African common bean varieties (GL) that comprise Andean and Mesoamerican genetic groups. An initial wide screening in modified Leonard jars (LJ) was followed by evaluation of a subset of strains and genotypes in pots (contained the same, sterile medium) in which fixed nitrogen was also quantified. An additive main effect and multiplicative interaction (AMMI) model was used to identify the contribution of individual strains and plant genotypes to the GL × GR interaction. Strong and highly significant GL × GR interaction was found in the LJ experiment but with little evidence of a relation to genetic background or growth habits. The interaction was much weaker in the pot experiment, with all bean genotypes and Rhizobium strains having relatively stable performance. We found that R. etli strain CFN42 and R. tropici strains CIAT899 and NAK91 were effective across bean genotypes but with the latter showing evidence of positive interaction with two specific bean genotypes. This suggests that selection of bean varieties based on their response to inoculation is possible. On the other hand, we show that symbiotic performance is not predicted by any a priori grouping, limiting the scope for more general recommendations. The fact that the strength and pattern of GL × GR depended on growing conditions provides an important cautionary message for future studies.IMPORTANCE The existence of genotype-by-strain (GL × GR) interaction has implications for the expected stability of performance of legume inoculants and could represent both challenges and opportunities for improvement of nitrogen fixation. We find that significant genotype-by-strain interaction exists in common bean (Phaseolus vulgaris L.) but that the strength and direction of this interaction depends on the growing environment used to evaluate biomass. Strong genotype and strain main effects, combined with a lack of predictable patterns in GL × GR, suggests that at best individual bean genotypes and strains can be selected for superior additive performance. The observation that the screening environment may affect experimental outcome of GL × GR means that identified patterns should be corroborated under more realistic conditions.
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Affiliation(s)
- A H Gunnabo
- Plant Production Systems Group, Wageningen University and Research, Wageningen, The Netherlands
| | - R Geurts
- Laboratory of Molecular Biology, Department of Plant Science, Wageningen University and Research, Wageningen, The Netherlands
| | - E Wolde-Meskel
- World Agroforestry Centre (ICRAF), Addis Ababa, Ethiopia
| | - T Degefu
- International Crops Research Institute for the Semi-Arid Tropics, Addis Ababa, Ethiopia
| | - K E Giller
- Plant Production Systems Group, Wageningen University and Research, Wageningen, The Netherlands
| | - J van Heerwaarden
- Plant Production Systems Group, Wageningen University and Research, Wageningen, The Netherlands
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Ford Denison R. Evolutionary trade-offs are key to beneficial manipulation of crops by microbes. AMERICAN JOURNAL OF BOTANY 2019; 106:1529-1531. [PMID: 31721158 DOI: 10.1002/ajb2.1386] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Accepted: 08/28/2019] [Indexed: 06/10/2023]
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Benezech C, Doudement M, Gourion B. Legumes tolerance to rhizobia is not always observed and not always deserved. Cell Microbiol 2019; 22:e13124. [DOI: 10.1111/cmi.13124] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 09/03/2019] [Accepted: 09/05/2019] [Indexed: 12/17/2022]
Affiliation(s)
- Claire Benezech
- LIPM, Université de Toulouse, INRA, CNRS Castanet‐Tolosan France
| | - Maëva Doudement
- LIPM, Université de Toulouse, INRA, CNRS Castanet‐Tolosan France
| | - Benjamin Gourion
- LIPM, Université de Toulouse, INRA, CNRS Castanet‐Tolosan France
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Microbial associations enabling nitrogen acquisition in plants. Curr Opin Microbiol 2019; 49:83-89. [DOI: 10.1016/j.mib.2019.10.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Revised: 10/03/2019] [Accepted: 10/11/2019] [Indexed: 01/29/2023]
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Iturralde ET, Covelli JM, Alvarez F, Pérez-Giménez J, Arrese-Igor C, Lodeiro AR. Soybean-Nodulating Strains With Low Intrinsic Competitiveness for Nodulation, Good Symbiotic Performance, and Stress-Tolerance Isolated From Soybean-Cropped Soils in Argentina. Front Microbiol 2019; 10:1061. [PMID: 31139173 PMCID: PMC6527597 DOI: 10.3389/fmicb.2019.01061] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 04/26/2019] [Indexed: 01/04/2023] Open
Abstract
Soybean is the most important oilseed in the world, cropped in 120–130 million hectares each year. The three most important soybean producers are Argentina, Brazil, and United States, where soybean crops are routinely inoculated with symbiotic N2-fixing Bradyrhizobium spp. This extended inoculation gave rise to soybean-nodulating allochthonous populations (SNAPs) that compete against new inoculant for nodulation, thus impairing yield responses. Competitiveness depends on intrinsic factors contributed by genotype, extrinsic ones determined by growth and environmental conditions, and strain persistence in the soil. To assess these factors in Argentinean SNAPs, we studied 58 isolates from five sites of the main soybean cropping area. BOX-A1R DNA fingerprint distributed these isolates in 10 clades that paralleled the pHs of their original soils. By contrast, reference Bradyrhizobium spp. strains, including those used as soybean-inoculants, were confined to a single clade. More detailed characterization of a subset of 11 SNAP-isolates revealed that five were Bradyrhizobium japonicum, two Bradyrhizobium elkanii, two Rhizobium radiobacter (formerly Agrobacterium tumefaciens), one Bradyrhizobium diazoefficiens, and one Paenibacillus glycanilyticus-which did not nodulate when inoculated alone, and therefore was excluded from further characterization. The remaining subset of 10 SNAP-isolates was used for deeper characterization. All SNAP-isolates were aluminum- and heat-tolerant, and most of them were glyphosate-tolerant. Meanwhile, inoculant strains tested were sensitive to aluminum and glyphosate. In addition, all SNAP-isolates were motile to different degrees. Only three SNAP-isolates were deficient for N2-fixation, and none was intrinsically more competitive than the inoculant strain. These results are in contrast to the general belief that rhizobia from soil populations evolved as intrinsically more competitive for nodulation and less N2-fixing effective than inoculants strains. Shoot:root ratios, both as dry biomass and as total N, were highly correlated with leaf ureide contents, and therefore may be easy indicators of N2-fixing performance, suggesting that highly effective N2-fixing and well-adapted strains may be readily selected from SNAPs. In addition, intrinsic competitiveness of the inoculants strains seems already optimized against SNAP strains, and therefore our efforts to improve nodules occupation by inoculated strains should focus on the optimization of extrinsic competitiveness factors, such as inoculant formulation and inoculation technology.
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Affiliation(s)
- Esteban T Iturralde
- Facultad de Ciencias Exactas, Instituto de Biotecnología y Biología Molecular (IBBM), UNLP y CCT La Plata-CONICET, La Plata, Argentina
| | - Julieta M Covelli
- Facultad de Ciencias Exactas, Instituto de Biotecnología y Biología Molecular (IBBM), UNLP y CCT La Plata-CONICET, La Plata, Argentina
| | - Florencia Alvarez
- Facultad de Ciencias Exactas, Instituto de Biotecnología y Biología Molecular (IBBM), UNLP y CCT La Plata-CONICET, La Plata, Argentina
| | - Julieta Pérez-Giménez
- Facultad de Ciencias Exactas, Instituto de Biotecnología y Biología Molecular (IBBM), UNLP y CCT La Plata-CONICET, La Plata, Argentina
| | - Cesar Arrese-Igor
- Institute for Multidisciplinary Research in Applied Biology (IMAB), Universidad Pública de Navarra, Pamplona, Spain
| | - Aníbal R Lodeiro
- Facultad de Ciencias Exactas, Instituto de Biotecnología y Biología Molecular (IBBM), UNLP y CCT La Plata-CONICET, La Plata, Argentina
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Clark TJ, Friel CA, Grman E, Friesen ML, Shachar-Hill Y. Unfair trade underground revealed by integrating data with Nash bargaining models. THE NEW PHYTOLOGIST 2019; 222:1325-1337. [PMID: 30671951 DOI: 10.1111/nph.15703] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2018] [Accepted: 01/08/2019] [Indexed: 06/09/2023]
Abstract
Mutually beneficial resource exchange is fundamental to global biogeochemical cycles and plant and animal nutrition. However, there is inherent potential conflict in mutualisms, as each organism benefits more when the exchange ratio ('price') minimizes its own costs and maximizes its benefits. Understanding the bargaining power that each partner has in these interactions is key to our ability to predict the exchange ratio and therefore the functionality of the cell, organism, community and ecosystem. We tested whether partners have symmetrical ('fair') or asymmetrical ('unfair') bargaining power in a legume-rhizobia nitrogen-fixing symbiosis using measurements of carbon and nitrogen dynamics in a mathematical modeling framework derived from economic theory. A model of symmetric bargaining power was not consistent with our data. Instead, our data indicate that the growth benefit to the plant (Medicago truncatula) has greater weight in determining trade dynamics than the benefit to the bacteria. Quantitative estimates of the relative power of the plant revealed that the plant's influence rises as soil nitrogen availability decreases and trade benefits to both partners increase. Our finding that M. truncatula legumes have more bargaining power than their rhizobial partner at lower nitrogen availabilities highlights the importance of context-dependence for the evolution of mutualism with increasing nutrient deposition.
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Affiliation(s)
- Teresa J Clark
- Department of Plant Biology, Michigan State University, 612 Wilson Rd., East Lansing, MI, 48824, USA
| | - Colleen A Friel
- Department of Plant Biology, Michigan State University, 612 Wilson Rd., East Lansing, MI, 48824, USA
| | - Emily Grman
- Department of Biology, Eastern Michigan University, 441 Mark Jefferson Science Complex, Ypsilanti, MI, 48197, USA
| | - Maren L Friesen
- Department of Plant Biology, Michigan State University, 612 Wilson Rd., East Lansing, MI, 48824, USA
- Department of Plant Pathology, Washington State University, Johnson Hall Rm 345, Pullman, WA, 99164, USA
- Department of Crop and Soil Sciences, Washington State University, Johnson Hall Rm 115, Pullman, WA, 99164, USA
| | - Yair Shachar-Hill
- Department of Plant Biology, Michigan State University, 612 Wilson Rd., East Lansing, MI, 48824, USA
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47
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Gano‐Cohen KA, Wendlandt CE, Stokes PJ, Blanton MA, Quides KW, Zomorrodian A, Adinata ES, Sachs JL. Interspecific conflict and the evolution of ineffective rhizobia. Ecol Lett 2019; 22:914-924. [DOI: 10.1111/ele.13247] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Accepted: 02/07/2019] [Indexed: 12/25/2022]
Affiliation(s)
- Kelsey A. Gano‐Cohen
- Department of Microbiology and Plant Pathology University of California Riverside CA USA
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Camille E. Wendlandt
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
- Department of Botany and Plant Sciences University of California Riverside CA USA
| | - Peter J. Stokes
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Mia A. Blanton
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Kenjiro W. Quides
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Avissa Zomorrodian
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Eunice S. Adinata
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Joel L. Sachs
- Department of Microbiology and Plant Pathology University of California Riverside CA USA
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
- Department of Botany and Plant Sciences University of California Riverside CA USA
- Institute for Integrative Genome Biology University of California Riverside CA USA
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48
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diCenzo GC, Zamani M, Checcucci A, Fondi M, Griffitts JS, Finan TM, Mengoni A. Multidisciplinary approaches for studying rhizobium–legume symbioses. Can J Microbiol 2019; 65:1-33. [DOI: 10.1139/cjm-2018-0377] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The rhizobium–legume symbiosis is a major source of fixed nitrogen (ammonia) in the biosphere. The potential for this process to increase agricultural yield while reducing the reliance on nitrogen-based fertilizers has generated interest in understanding and manipulating this process. For decades, rhizobium research has benefited from the use of leading techniques from a very broad set of fields, including population genetics, molecular genetics, genomics, and systems biology. In this review, we summarize many of the research strategies that have been employed in the study of rhizobia and the unique knowledge gained from these diverse tools, with a focus on genome- and systems-level approaches. We then describe ongoing synthetic biology approaches aimed at improving existing symbioses or engineering completely new symbiotic interactions. The review concludes with our perspective of the future directions and challenges of the field, with an emphasis on how the application of a multidisciplinary approach and the development of new methods will be necessary to ensure successful biotechnological manipulation of the symbiosis.
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Affiliation(s)
- George C. diCenzo
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
| | - Maryam Zamani
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Alice Checcucci
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
| | - Marco Fondi
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
| | - Joel S. Griffitts
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA
| | - Turlough M. Finan
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Alessio Mengoni
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
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49
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Berrabah F, Ratet P, Gourion B. Legume Nodules: Massive Infection in the Absence of Defense Induction. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2019; 32:35-44. [PMID: 30252618 DOI: 10.1094/mpmi-07-18-0205-fi] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Plants of the legume family host massive intracellular bacterial populations in the tissues of specialized organs, the nodules. In these organs, the bacteria, named rhizobia, can fix atmospheric nitrogen and transfer it to the plant. This special metabolic skill provides to the legumes an advantage when they grow on nitrogen-scarce substrates. While packed with rhizobia, the nodule cells remain alive, metabolically active, and do not develop defense reactions. Here, we review our knowledge on the control of plant immunity during the rhizobia-legume symbiosis. We present the results of an evolutionary process that selected both divergence of microbial-associated molecular motifs and active suppressors of immunity on the rhizobial side and, on the legume side, active mechanisms that contribute to suppression of immunity.
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Affiliation(s)
- Fathi Berrabah
- 1 Laboratory of Exploration and Valorization of Steppic Ecosystems, Faculty of Nature and Life Sciences, University of Ziane Achour, 17000 Djelfa, Algeria
| | - Pascal Ratet
- 2 Institute of Plant Sciences Paris-Saclay IPS2, CNRS, INRA, Université Paris-Sud, Université Evry, Université Paris-Saclay, Bâtiment 630, 91405 Orsay, France
- 3 Institute of Plant Sciences Paris-Saclay IPS2, Paris Diderot, Sorbonne Paris-Cité, Bâtiment 630, 91405, Orsay, France; and
| | - Benjamin Gourion
- 4 LIPM, Université de Toulouse, INRA, CNRS, Castanet-Tolosan, France
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50
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Porter SS, Faber-Hammond J, Montoya AP, Friesen ML, Sackos C. Dynamic genomic architecture of mutualistic cooperation in a wild population of Mesorhizobium. ISME JOURNAL 2018; 13:301-315. [PMID: 30218020 PMCID: PMC6331556 DOI: 10.1038/s41396-018-0266-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Revised: 07/01/2018] [Accepted: 08/04/2018] [Indexed: 12/14/2022]
Abstract
Research on mutualism seeks to explain how cooperation can be maintained when uncooperative mutants co-occur with cooperative kin. Gains and losses of the gene modules required for cooperation punctuate symbiont phylogenies and drive lifestyle transitions between cooperative symbionts and uncooperative free-living lineages over evolutionary time. Yet whether uncooperative symbionts commonly evolve from within cooperative symbiont populations or from within distantly related lineages with antagonistic or free-living lifestyles (i.e., third-party mutualism exploiters or parasites), remains controversial. We use genomic data to show that genotypes that differ in the presence or absence of large islands of symbiosis genes are common within a single wild recombining population of Mesorhizobium symbionts isolated from host tissues and are an important source of standing heritable variation in cooperation in this population. In a focal population of Mesorhizobium, uncooperative variants that lack a symbiosis island segregate at 16% frequency in nodules, and genome size and symbiosis gene number are positively correlated with cooperation. This finding contrasts with the genomic architecture of variation in cooperation in other symbiont populations isolated from host tissues in which the islands of genes underlying cooperation are ubiquitous and variation in cooperation is primarily driven by allelic substitution and individual gene gain and loss events. Our study demonstrates that uncooperative mutants within mutualist populations can comprise a significant component of genetic variation in nature, providing biological rationale for models and experiments that seek to explain the maintenance of mutualism in the face of non-cooperators.
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Affiliation(s)
- Stephanie S Porter
- School of Biological Sciences, Washington State University, Vancouver, WA, 98686, USA.
| | - Joshua Faber-Hammond
- School of Biological Sciences, Washington State University, Vancouver, WA, 98686, USA
| | - Angeliqua P Montoya
- School of Biological Sciences, Washington State University, Vancouver, WA, 98686, USA
| | - Maren L Friesen
- Department of Plant Biology, Michigan State University, East Lansing, MI, 48824, USA.,Department of Plant Pathology, Washington State University, Pullman, WA, 99164, USA.,Department of Crop and Soil Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Cynthia Sackos
- School of Biological Sciences, Washington State University, Vancouver, WA, 98686, USA
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