1
|
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.
Collapse
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.
| |
Collapse
|
2
|
Brescia F, Sillo F, Franchi E, Pietrini I, Montesano V, Marino G, Haworth M, Zampieri E, Fusini D, Schillaci M, Papa R, Santamarina C, Vita F, Chitarra W, Nerva L, Petruzzelli G, Mennone C, Centritto M, Balestrini R. The 'microbiome counterattack': Insights on the soil and root-associated microbiome in diverse chickpea and lentil genotypes after an erratic rainfall event. ENVIRONMENTAL MICROBIOLOGY REPORTS 2023; 15:459-483. [PMID: 37226644 PMCID: PMC10667653 DOI: 10.1111/1758-2229.13167] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2023] [Accepted: 05/05/2023] [Indexed: 05/26/2023]
Abstract
Legumes maintain soil fertility thanks to their associated microbiota but are threatened by climate change that causes soil microbial community structural and functional modifications. The core microbiome associated with different chickpea and lentil genotypes was described after an unexpected climatic event. Results showed that chickpea and lentil bulk soil microbiomes varied significantly between two sampling time points, the first immediately after the rainfall and the second 2 weeks later. Rhizobia were associated with the soil of the more productive chickpea genotypes in terms of flower and fruit number. The root-associated bacteria and fungi were surveyed in lentil genotypes, considering that several parcels showed disease symptoms. The metabarcoding analysis revealed that reads related to fungal pathogens were significantly associated with one lentil genotype. A lentil core prokaryotic community common to all genotypes was identified as well as a genotype-specific one. A higher number of specific bacterial taxa and an enhanced tolerance to fungal diseases characterized a lentil landrace compared to the commercial varieties. This outcome supported the hypothesis that locally adapted landraces might have a high recruiting efficiency of beneficial soil microbes.
Collapse
Affiliation(s)
- Francesca Brescia
- Institute for Sustainable Plant ProtectionNational Research Council of ItalyTurinItaly
| | - Fabiano Sillo
- Institute for Sustainable Plant ProtectionNational Research Council of ItalyTurinItaly
| | - Elisabetta Franchi
- Eni S.p.A.R&D Environmental & Biological LaboratoriesSan Donato MilaneseItaly
| | - Ilaria Pietrini
- Eni S.p.A.R&D Environmental & Biological LaboratoriesSan Donato MilaneseItaly
| | - Vincenzo Montesano
- Institute for Sustainable Plant ProtectionNational Research Council of ItalyBernalda (MT)Italy
| | - Giovanni Marino
- Institute for Sustainable Plant ProtectionNational Research Council of ItalySesto FiorentinoItaly
| | - Matthew Haworth
- Institute for Sustainable Plant ProtectionNational Research Council of ItalySesto FiorentinoItaly
| | - Elisa Zampieri
- Institute for Sustainable Plant ProtectionNational Research Council of ItalyTurinItaly
| | - Danilo Fusini
- Eni S.p.A.R&D Environmental & Biological LaboratoriesSan Donato MilaneseItaly
| | - Martino Schillaci
- Institute for Sustainable Plant ProtectionNational Research Council of ItalyTurinItaly
| | - Roberto Papa
- Department of Agricultural, Food and Environmental SciencesPolytechnic University of MarcheAnconaItaly
| | - Chiara Santamarina
- Department of Agricultural, Food and Environmental SciencesPolytechnic University of MarcheAnconaItaly
| | - Federico Vita
- Department of Bioscience, Biotechnology and EnvironmentUniversity of Bari Aldo MoroBariItaly
| | - Walter Chitarra
- Research Centre for Viticulture and EnologyCouncil for Agricultural Research and EconomicsConeglianoItaly
| | - Luca Nerva
- Research Centre for Viticulture and EnologyCouncil for Agricultural Research and EconomicsConeglianoItaly
| | | | - Carmelo Mennone
- Azienda Pantanello, ALSIA Research Center Metapontum AgrobiosBernalda (MT)Italy
| | - Mauro Centritto
- Institute for Sustainable Plant ProtectionNational Research Council of ItalySesto FiorentinoItaly
- ENI‐CNR Water Research Center ‘Hypatia of Alexandria’ALSIA Research Center Metapontum AgrobiosBernaldaItaly
| | - Raffaella Balestrini
- Institute for Sustainable Plant ProtectionNational Research Council of ItalyTurinItaly
- ENI‐CNR Water Research Center ‘Hypatia of Alexandria’ALSIA Research Center Metapontum AgrobiosBernaldaItaly
| |
Collapse
|
3
|
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.
Collapse
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
| |
Collapse
|
4
|
Genome-Wide Association Studies across Environmental and Genetic Contexts Reveal Complex Genetic Architecture of Symbiotic Extended Phenotypes. mBio 2022; 13:e0182322. [PMID: 36286519 PMCID: PMC9765617 DOI: 10.1128/mbio.01823-22] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A goal of modern biology is to develop the genotype-phenotype (G→P) map, a predictive understanding of how genomic information generates trait variation that forms the basis of both natural and managed communities. As microbiome research advances, however, it has become clear that many of these traits are symbiotic extended phenotypes, being governed by genetic variation encoded not only by the host's own genome, but also by the genomes of myriad cryptic symbionts. Building a reliable G→P map therefore requires accounting for the multitude of interacting genes and even genomes involved in symbiosis. Here, we use naturally occurring genetic variation in 191 strains of the model microbial symbiont Sinorhizobium meliloti paired with two genotypes of the host Medicago truncatula in four genome-wide association studies (GWAS) to determine the genomic architecture of a key symbiotic extended phenotype-partner quality, or the fitness benefit conferred to a host by a particular symbiont genotype, within and across environmental contexts and host genotypes. We define three novel categories of loci in rhizobium genomes that must be accounted for if we want to build a reliable G→P map of partner quality; namely, (i) loci whose identities depend on the environment, (ii) those that depend on the host genotype with which rhizobia interact, and (iii) universal loci that are likely important in all or most environments. IMPORTANCE Given the rapid rise of research on how microbiomes can be harnessed to improve host health, understanding the contribution of microbial genetic variation to host phenotypic variation is pressing, and will better enable us to predict the evolution of (and select more precisely for) symbiotic extended phenotypes that impact host health. We uncover extensive context-dependency in both the identity and functions of symbiont loci that control host growth, which makes predicting the genes and pathways important for determining symbiotic outcomes under different conditions more challenging. Despite this context-dependency, we also resolve a core set of universal loci that are likely important in all or most environments, and thus, serve as excellent targets both for genetic engineering and future coevolutionary studies of symbiosis.
Collapse
|
5
|
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.
Collapse
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
| |
Collapse
|
6
|
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.
Collapse
Affiliation(s)
- R. Ford Denison
- Ecology, Evolution, & BehaviorUniversity of MinnesotaSaint PaulMinnesotaUSA
| | | |
Collapse
|
7
|
Burghardt LT, Epstein B, Hoge M, Trujillo DI, Tiffin P. Host-Associated Rhizobial Fitness: Dependence on Nitrogen, Density, Community Complexity, and Legume Genotype. Appl Environ Microbiol 2022; 88:e0052622. [PMID: 35852362 PMCID: PMC9361818 DOI: 10.1128/aem.00526-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Accepted: 06/24/2022] [Indexed: 11/20/2022] Open
Abstract
The environmental context of the nitrogen-fixing mutualism between leguminous plants and rhizobial bacteria varies over space and time. Variation in resource availability, population density, and composition likely affect the ecology and evolution of rhizobia and their symbiotic interactions with hosts. We examined how host genotype, nitrogen addition, rhizobial density, and community complexity affected selection on 68 rhizobial strains in the Sinorhizobium meliloti-Medicago truncatula mutualism. As expected, host genotype had a substantial effect on the size, number, and strain composition of root nodules (the symbiotic organ). The understudied environmental variable of rhizobial density had a stronger effect on nodule strain frequency than the addition of low nitrogen levels. Higher inoculum density resulted in a nodule community that was less diverse and more beneficial but only in the context of the more selective host genotype. Higher density resulted in more diverse and less beneficial nodule communities with the less selective host. Density effects on strain composition deserve additional scrutiny as they can create feedback between ecological and evolutionary processes. Finally, we found that relative strain rankings were stable across increasing community complexity (2, 3, 8, or 68 strains). This unexpected result suggests that higher-order interactions between strains are rare in the context of nodule formation and development. Our work highlights the importance of examining mechanisms of density-dependent strain fitness and developing theoretical predictions that incorporate density dependence. Furthermore, our results have translational relevance for overcoming establishment barriers in bioinoculants and motivating breeding programs that maintain beneficial plant-microbe interactions across diverse agroecological contexts. IMPORTANCE Legume crops establish beneficial associations with rhizobial bacteria that perform biological nitrogen fixation, providing nitrogen to plants without the economic and greenhouse gas emission costs of chemical nitrogen inputs. Here, we examine the influence of three environmental factors that vary in agricultural fields on strain relative fitness in nodules. In addition to manipulating nitrogen, we also use two biotic variables that have rarely been examined: the rhizobial community's density and complexity. Taken together, our results suggest that (i) breeding legume varieties that select beneficial strains despite environmental variation is possible, (ii) changes in rhizobial population densities that occur routinely in agricultural fields could drive evolutionary changes in rhizobial populations, and (iii) the lack of higher-order interactions between strains will allow the high-throughput assessments of rhizobia winners and losers during plant interactions.
Collapse
Affiliation(s)
- Liana T. Burghardt
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
- Plant Science Department, The Pennsylvania State University, University Park, Pennsylvania, USA
| | - Brendan Epstein
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - Michelle Hoge
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - Diana I. Trujillo
- 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
| |
Collapse
|
8
|
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.
Collapse
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.
| |
Collapse
|
9
|
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.
Collapse
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
| |
Collapse
|
10
|
Triki Z, Richter XYL, Demairé C, Kurokawa S, Bshary R. Marine cleaning mutualism defies standard logic of supply and demand. Am Nat 2021; 199:455-467. [DOI: 10.1086/718315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
|
11
|
The direct and interactive effects of elevated CO2 and additional nitrate on relative costs and benefits of legume-rhizobia symbiosis. Symbiosis 2021. [DOI: 10.1007/s13199-021-00784-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
AbstractRising concentrations of carbon dioxide (CO2) is likely to have important effects on growth and development of plants and on their relationship with symbiotic microbes. A rise in CO2 could increase demand by plant hosts for nutrient resources, which may increase host investments in beneficial symbionts. In the legume-rhizobia mutualism, while elevated CO2 is often associated with increased nodule growth and investment in N2-fixing rhizobia, it is yet unclear if this response depends on the mutualistic quality of the rhizobia. To test if host carbon allocation towards more-beneficial nodules are similar to less-beneficial (but still effective) nodules when plant N demand changes, we manipulated plant C and N status with elevated CO2 and additional nitrate. We used two isogenic Rhizobium etli strains that differ in their ability to synthesize an energy reserve compound, poly-beta-hydroxybutyrate (PHB), as well as their efficiencies for nitrogen fixation and nodulation rates, resulting in two Phaseolus vulgaris host groups with either large number of small nodules or small number of large nodules. The addition of nitrate negatively affected carbon allocation towards nodules, and elevated CO2 reversed this effect, as expected. However, this alleviation of nodule inhibition was greater on plants that started with greater numbers of smaller nodules. If smaller nodules indicate less-efficient or low-fixing rhizobia, this study suggests that increased demand for nitrogen in the face of elevated CO2 has the potential to disproportionately favor less-beneficial strains and increase variation of nitrogen fixation quality among rhizobia.
Collapse
|
12
|
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.
Collapse
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
| |
Collapse
|
13
|
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.
Collapse
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;
| |
Collapse
|
14
|
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.
Collapse
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
| |
Collapse
|
15
|
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.
Collapse
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
| |
Collapse
|
16
|
Oono R, Muller KE, Ho R, Jimenez Salinas A, Denison RF. How do less-expensive nitrogen alternatives affect legume sanctions on rhizobia? Ecol Evol 2020; 10:10645-10656. [PMID: 33072286 PMCID: PMC7548176 DOI: 10.1002/ece3.6718] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Revised: 07/29/2020] [Accepted: 07/29/2020] [Indexed: 01/28/2023] Open
Abstract
The evolutionary stability of mutualistic interactions involving multiple partners requires “sanctioning”–the ability to influence the fitness of each partner based on its respective contribution. Sanctions must be sensitive to even small differences if even slightly less‐beneficial partners could gain a fitness advantage by diverting resources away from the mutualistic service toward their own reproductive fitness. Here, we test whether legume hosts sanction even mediocre N2‐fixing rhizobial strains by influencing either nodule growth (which limits rhizobial cell numbers) or carbon accumulation (polyhydroxybutryate or PHB) per rhizobial cell. We also test whether sanctions depend on the availability of less‐expensive nitrogen alternatives, either as nitrate or coinoculation with a more‐efficient isogenic strain. We found that nitrate eliminated differences in nodule size between the mediocre and more‐efficient strains, suggesting that host sanctions were compromised. However, nitrate additions also decreased PHB accumulation by the mediocre strain, which may eliminate any fitness advantages of diverting resources from N2 fixation. Coinoculation with a more‐efficient strain could also compromise host sanctions if reduction in fitness from smaller nodules does not offset the potential fitness gain from greater PHB accumulation that we observed in the mediocre strain. Hence, a host's ability to sanction mediocre strains depends not only on alternative sources of nitrogen but also the relative importance of different components of rhizobial fitness.
Collapse
Affiliation(s)
- Ryoko Oono
- Department of Ecology, Evolution, and Marine Biology University of California Santa Barbara CA USA
| | - Katherine E Muller
- Department of Ecology, Evolution, and Behavior University of Minnesota - Twin Cities St. Paul MN USA.,Present address: School of Integrated Sciences Cornell University Ithaca NY USA
| | - Randy Ho
- Department of Ecology, Evolution, and Marine Biology University of California Santa Barbara CA USA
| | - Andres Jimenez Salinas
- Department of Ecology, Evolution, and Marine Biology University of California Santa Barbara CA USA.,Department of Chemistry and Biochemistry San Diego State University San Diego CA USA
| | - Robert Ford Denison
- Department of Ecology, Evolution, and Behavior University of Minnesota - Twin Cities St. Paul MN USA
| |
Collapse
|
17
|
Burghardt LT. Evolving together, evolving apart: measuring the fitness of rhizobial bacteria in and out of symbiosis with leguminous plants. THE NEW PHYTOLOGIST 2020; 228:28-34. [PMID: 31276218 DOI: 10.1111/nph.16045] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Accepted: 06/20/2019] [Indexed: 05/11/2023]
Abstract
Most plant-microbe interactions are facultative, with microbes experiencing temporally and spatially variable selection. How this variation affects microbial evolution is poorly understood. Given its tractability and ecological and agricultural importance, the legume-rhizobia nitrogen-fixing symbiosis is a powerful model for identifying traits and genes underlying bacterial fitness. New technologies allow high-throughput measurement of the relative fitness of bacterial mutants, strains and species in mixed inocula in the host, rhizosphere and soil environments. I consider how host genetic variation (G × G), other environmental factors (G × E), and host life-cycle variation may contribute to the maintenance of genetic variation and adaptive trajectories of rhizobia - and, potentially, other facultative symbionts. Lastly, I place these findings in the context of developing beneficial inoculants in a changing climate.
Collapse
Affiliation(s)
- Liana T Burghardt
- Department of Plant and Microbial Biology, University of Minnesota, 140 Gortner Laboratory, 1479 Gortner Avenue, St Paul, MN, 55108, USA
| |
Collapse
|
18
|
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.
Collapse
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
| |
Collapse
|
19
|
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.
Collapse
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
| |
Collapse
|
20
|
Heath KD, Podowski JC, Heniff S, Klinger CR, Burke PV, Weese DJ, Yang WH, Lau JA. Light availability and rhizobium variation interactively mediate the outcomes of legume-rhizobium symbiosis. AMERICAN JOURNAL OF BOTANY 2020; 107:229-238. [PMID: 32072629 DOI: 10.1002/ajb2.1435] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2019] [Accepted: 12/08/2019] [Indexed: 05/22/2023]
Abstract
PREMISE Nutrients, light, water, and temperature are key factors limiting the growth of individual plants in nature. Mutualistic interactions between plants and microbes often mediate resource limitation for both partners. In the mutualism between legumes and rhizobia, plants provide rhizobia with carbon in exchange for fixed nitrogen. Because partner quality in mutualisms is genotype-dependent, within-species genetic variation is expected to alter the responses of mutualists to changes in the resource environment. Here we ask whether partner quality variation in rhizobia mediates the response of host plants to changing light availability, and conversely, whether light alters the expression of partner quality variation. METHODS We inoculated clover hosts with 11 strains of Rhizobium leguminosarum that differed in partner quality, grew plants under either ambient or low light conditions in the greenhouse, and measured plant growth, nodule traits, and foliar nutrient composition. RESULTS Light availability and rhizobium inoculum interactively determined plant growth, and variation in rhizobium partner quality was more apparent in ambient light. CONCLUSIONS Our results suggest that variation in the costs and benefits of rhizobium symbionts mediate host responses to light availability and that rhizobium strain variation might more important in higher-light environments. Our work adds to a growing appreciation for the role of microbial intraspecific and interspecific diversity in mediating extended phenotypes in their hosts and suggests an important role for light availability in the ecology and evolution of legume-rhizobium symbiosis.
Collapse
Affiliation(s)
- Katy D Heath
- Department of Plant Biology, University of Illinois at Urbana-Champaign, 505 S. Goodwin Ave., Urbana, IL, 61801, USA
| | - Justin C Podowski
- Department of Plant Biology, University of Illinois at Urbana-Champaign, 505 S. Goodwin Ave., Urbana, IL, 61801, USA
| | - Stephanie Heniff
- Department of Plant Biology, University of Illinois at Urbana-Champaign, 505 S. Goodwin Ave., Urbana, IL, 61801, USA
| | - Christie R Klinger
- Department of Plant Biology, University of Illinois at Urbana-Champaign, 505 S. Goodwin Ave., Urbana, IL, 61801, USA
| | - Patricia V Burke
- Department of Plant Biology, University of Illinois at Urbana-Champaign, 505 S. Goodwin Ave., Urbana, IL, 61801, USA
| | - Dylan J Weese
- Department of Biology, St. Ambrose University, Davenport, IA, 52803, USA
| | - Wendy H Yang
- Department of Plant Biology, University of Illinois at Urbana-Champaign, 505 S. Goodwin Ave., Urbana, IL, 61801, USA
| | - Jennifer A Lau
- W. K. Kellogg Biological Station and Department of Plant Biology, Michigan State University, East Lansing, MI, 48824, USA
| |
Collapse
|
21
|
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.
Collapse
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
| |
Collapse
|
22
|
Adaptive partner recruitment can help maintain an intra-guild diversity in mutualistic systems. J Theor Biol 2019; 478:40-47. [PMID: 31220467 DOI: 10.1016/j.jtbi.2019.06.017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Revised: 06/13/2019] [Accepted: 06/17/2019] [Indexed: 11/20/2022]
Abstract
Mutualisms between assemblages of multiple species or strains (guilds) are considered unstable because of positive feedback between the guilds. Previous studies suggest that negative inter-guild feedback due to asymmetry in the exchange of benefits between the guilds can stabilize them, but preferential association for more beneficial partners may reduce such asymmetry and strengthen the positive inter-guild feedback. Here I develop a replicator dynamics model for mutualistic systems between two host and two symbiont strains to investigate conditions that stabilize mutualisms when feedback between host-symbiont guilds is positive. I assume that one symbiont strain is mutualistic for one host strain but parasitic for the other, whereas the other symbiont strain is the opposite. Hosts recruit their symbionts from the environment and discriminately offer them resources (partner preference), and only mutualistic symbionts return benefits to their hosts. I show that the two host and symbiont strains can coexist under strong partner preference by hosts if they adaptively adjust the number of associating symbionts, even when the intra-host strain competition is not so strong. Interestingly, there can be a stable coexistence equilibrium also under weak partner preference, but it disappears under intermediate levels of partner preference.
Collapse
|
23
|
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
| |
Collapse
|
24
|
Wendlandt CE, Regus JU, Gano-Cohen KA, Hollowell AC, Quides KW, Lyu JY, Adinata ES, Sachs JL. Host investment into symbiosis varies among genotypes of the legume Acmispon strigosus, but host sanctions are uniform. THE NEW PHYTOLOGIST 2019; 221:446-458. [PMID: 30084172 DOI: 10.1111/nph.15378] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Accepted: 07/05/2018] [Indexed: 05/26/2023]
Abstract
Efficient host control predicts the extirpation of ineffective symbionts, but they are nonetheless widespread in nature. We tested three hypotheses for the maintenance of symbiotic variation in rhizobia that associate with a native legume: partner mismatch between host and symbiont, such that symbiont effectiveness varies with host genotype; resource satiation, whereby extrinsic sources of nutrients relax host control; and variation in host control among host genotypes. We inoculated Acmispon strigosus from six populations with three Bradyrhizobium strains that vary in symbiotic effectiveness on sympatric hosts. We measured proxies of host and symbiont fitness in single- and co-inoculations under fertilization treatments of zero added nitrogen (N) and near-growth-saturating N. We examined two components of host control: 'host investment' into nodule size during single- and co-inoculations, and 'host sanctions' against less effective strains during co-inoculations. The Bradyrhizobium strains displayed conserved growth effects on hosts, and host control did not decline under experimental fertilization. Host sanctions were robust in all hosts, but host lines from different populations varied significantly in measures of host investment in both single- and co-inoculation experiments. Variation in host investment could promote variation in symbiotic effectiveness and prevent the extinction of ineffective Bradyrhizobium from natural populations.
Collapse
Affiliation(s)
- Camille E Wendlandt
- Department of Botany & Plant Sciences, University of California, Riverside, CA, 92521, USA
| | - John U Regus
- Department of Evolution, Ecology & Organismal Biology, University of California, Riverside, CA, 92521, USA
| | - Kelsey A Gano-Cohen
- Department of Microbiology & Plant Pathology, University of California, Riverside, CA, 92521, USA
| | - Amanda C Hollowell
- Department of Evolution, Ecology & Organismal Biology, University of California, Riverside, CA, 92521, USA
- Institute for Integrative Genome Biology, University of California, Riverside, CA, 92521, USA
| | - Kenjiro W Quides
- Department of Evolution, Ecology & Organismal Biology, University of California, Riverside, CA, 92521, USA
| | - Jonathan Y Lyu
- Department of Evolution, Ecology & Organismal Biology, University of California, Riverside, CA, 92521, USA
| | - Eunice S Adinata
- Department of Evolution, Ecology & Organismal Biology, University of California, Riverside, CA, 92521, USA
| | - Joel L Sachs
- Department of Botany & Plant Sciences, University of California, Riverside, CA, 92521, USA
- Department of Evolution, Ecology & Organismal Biology, University of California, Riverside, CA, 92521, USA
- Department of Microbiology & Plant Pathology, University of California, Riverside, CA, 92521, USA
- Institute for Integrative Genome Biology, University of California, Riverside, CA, 92521, USA
| |
Collapse
|
25
|
Pahua VJ, Stokes PJN, Hollowell AC, Regus JU, Gano‐Cohen KA, Wendlandt CE, Quides KW, Lyu JY, Sachs JL. Fitness variation among host species and the paradox of ineffective rhizobia. J Evol Biol 2018; 31:599-610. [DOI: 10.1111/jeb.13249] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Revised: 01/12/2018] [Accepted: 01/29/2018] [Indexed: 01/31/2023]
Affiliation(s)
- V. J. Pahua
- Department of Evolution Ecology and Organismal Biology University of California Riverside CA USA
| | - P. J. N. Stokes
- Department of Botany and Plant Sciences University of California Riverside CA USA
| | - A. C. Hollowell
- Department of Evolution Ecology and Organismal Biology University of California Riverside CA USA
| | - J. U. Regus
- Department of Evolution Ecology and Organismal Biology University of California Riverside CA USA
| | - K. A. Gano‐Cohen
- Department of Evolution Ecology and Organismal Biology University of California Riverside CA USA
| | - C. E. Wendlandt
- Department of Botany and Plant Sciences University of California Riverside CA USA
| | - K. W. Quides
- Department of Evolution Ecology and Organismal Biology University of California Riverside CA USA
| | - J. Y. Lyu
- Department of Evolution Ecology and Organismal Biology University of California Riverside CA USA
| | - J. L. Sachs
- Department of Evolution Ecology and 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
| |
Collapse
|
26
|
Forrester NJ, Ashman TL. The direct effects of plant polyploidy on the legume-rhizobia mutualism. ANNALS OF BOTANY 2018; 121:209-220. [PMID: 29182713 PMCID: PMC5808787 DOI: 10.1093/aob/mcx121] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Accepted: 09/08/2017] [Indexed: 05/09/2023]
Abstract
BACKGROUND Polyploidy is known to significantly alter plant genomes, phenotypes and interactions with the abiotic environment, yet the impacts of polyploidy on plant-biotic interactions are less well known. A particularly important plant-biotic interaction is the legume-rhizobia mutualism, in which rhizobia fix atmospheric nitrogen in exchange for carbon provided by legume hosts. This mutualism regulates nutrient cycles in natural ecosystems and provides nitrogen to agricultural environments. Despite the ecological, evolutionary and agricultural importance of plant polyploidy and the legume-rhizobia mutualism, it is not yet fully understood whether plant polyploidy directly alters mutualism traits or the consequences on plant growth. SCOPE The aim was to propose a conceptual framework to understand how polyploidy might directly enhance the quantity and quality of rhizobial symbionts hosted by legume plants, resulting in increased host access to fixed nitrogen (N). Mechanistic hypotheses have been devised to examine how polyploidy can directly alter traits that impact the quantity (e.g. nodule number, nodule size, terminal bacteroid differentiation) and quality of symbionts (e.g. nodule environment, partner choice, host sanctions). To evaluate these hypotheses, an exhaustive review of studies testing the effects of plant polyploidy on the mutualism was conducted. In doing so, overall trends were synthesized, highlighting the limited understanding of the mechanisms that underlie variation in results achieved thus far, revealing striking gaps in knowledge and uncovering areas ripe for future research. CONCLUSIONS Plant polyploidy can immediately alter nodule size, N fixation rate and the identity of rhizobial symbionts hosted by polyploid legumes, but many of the mechanistic hypotheses proposed here, such as bacteroid number and enhancements of the nodule environment, remain unexplored. Although current evidence supports a role of plant polyploidy in enhancing key aspects of the legume-rhizobia mutualism, the underlying mechanisms and effects on host benefit from the mutualism remain unresolved.
Collapse
Affiliation(s)
- Nicole J Forrester
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA
- For correspondence. E-mail
| | - Tia-Lynn Ashman
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| |
Collapse
|
27
|
Werner GDA, Zhou Y, Pieterse CMJ, Kiers ET. Tracking plant preference for higher-quality mycorrhizal symbionts under varying CO 2 conditions over multiple generations. Ecol Evol 2018; 8:78-87. [PMID: 29321853 PMCID: PMC5756855 DOI: 10.1002/ece3.3635] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Revised: 10/13/2017] [Accepted: 10/16/2017] [Indexed: 01/14/2023] Open
Abstract
The symbiosis between plants and root-colonizing arbuscular mycorrhizal (AM) fungi is one of the most ecologically important examples of interspecific cooperation in the world. AM fungi provide benefits to plants; in return plants allocate carbon resources to fungi, preferentially allocating more resources to higher-quality fungi. However, preferential allocations from plants to symbionts may vary with environmental context, particularly when resource availability affects the relative value of symbiotic services. We ask how differences in atmospheric CO 2-levels influence root colonization dynamics between AMF species that differ in their quality as symbiotic partners. We find that with increasing CO 2-conditions and over multiple plant generations, the more beneficial fungal species is able to achieve a relatively higher abundance. This suggests that increasing atmospheric carbon supply enables plants to more effectively allocate carbon to higher-quality mutualists, and over time helps reduce lower-quality AM abundance. Our results illustrate how environmental context may affect the extent to which organisms structure interactions with their mutualistic partners and have potential implications for mutualism stability and persistence under global change.
Collapse
Affiliation(s)
- Gijsbert D. A. Werner
- Department of Ecological ScienceVrije Universiteit AmsterdamAmsterdamThe Netherlands
- Department of ZoologyUniversity of OxfordOxfordUK
| | - Yeling Zhou
- Plant‐Microbe InteractionsDepartment of BiologyUtrecht UniversityUtrechtThe Netherlands
| | - Corné M. J. Pieterse
- Plant‐Microbe InteractionsDepartment of BiologyUtrecht UniversityUtrechtThe Netherlands
| | - E. Toby Kiers
- Department of Ecological ScienceVrije Universiteit AmsterdamAmsterdamThe Netherlands
| |
Collapse
|
28
|
Yoder JB, Tiffin P. Sanctions, Partner Recognition, and Variation in Mutualism. Am Nat 2017; 190:491-505. [DOI: 10.1086/693472] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
|
29
|
Quides KW, Stomackin GM, Lee HH, Chang JH, Sachs JL. Lotus japonicus alters in planta fitness of Mesorhizobium loti dependent on symbiotic nitrogen fixation. PLoS One 2017; 12:e0185568. [PMID: 28957401 PMCID: PMC5619806 DOI: 10.1371/journal.pone.0185568] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 09/14/2017] [Indexed: 12/19/2022] Open
Abstract
Rhizobial bacteria are known for their capacity to fix nitrogen for legume hosts. However ineffective rhizobial genotypes exist and can trigger the formation of nodules but fix little if any nitrogen for hosts. Legumes must employ mechanisms to minimize exploitation by the ineffective rhizobial genotypes to limit fitness costs and stabilize the symbiosis. Here we address two key questions about these host mechanisms. What stages of the interaction are controlled by the host, and can hosts detect subtle differences in nitrogen fixation? We provide the first explicit evidence for adaptive host control in the interaction between Lotus japonicus and Mesorhizobium loti. In both single inoculation and co-inoculation experiments, less effective rhizobial strains exhibited reduced in planta fitness relative to the wildtype M. loti. We uncovered evidence of host control during nodule formation and during post-infection proliferation of symbionts within nodules. We found a linear relationship between rhizobial fitness and symbiotic effectiveness. Our results suggest that L. japonicus can adaptively modulate the fitness of symbionts as a continuous response to symbiotic nitrogen fixation.
Collapse
Affiliation(s)
- Kenjiro W. Quides
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, United States of America
| | - Glenna M. Stomackin
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, United States of America
| | - Hsu-Han Lee
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, United States of America
| | - Jeff H. Chang
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, United States of America
| | - Joel L. Sachs
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, United States of America
- Department of Botany and Plant Sciences, University of California, Riverside, CA, United States of America
- Institute for Integrative Genome Biology, University of California, Riverside, CA, United States of America
- * E-mail:
| |
Collapse
|
30
|
Regus JU, Quides KW, O'Neill MR, Suzuki R, Savory EA, Chang JH, Sachs JL. Cell autonomous sanctions in legumes target ineffective rhizobia in nodules with mixed infections. AMERICAN JOURNAL OF BOTANY 2017; 104:1299-1312. [PMID: 29885243 DOI: 10.3732/ajb.1700165] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 08/11/2017] [Indexed: 05/22/2023]
Affiliation(s)
- John U. Regus
- Department of Evolution, Ecology, and Organismal Biology, 2710 Life Sciences Building, University of California, Riverside, California 92521 USA
| | - Kenjiro W. Quides
- Department of Evolution, Ecology, and Organismal Biology, 2710 Life Sciences Building, University of California, Riverside, California 92521 USA
| | - Matthew R. O'Neill
- Department of Evolution, Ecology, and Organismal Biology, 2710 Life Sciences Building, University of California, Riverside, California 92521 USA
| | - Rina Suzuki
- Department of Evolution, Ecology, and Organismal Biology, 2710 Life Sciences Building, University of California, Riverside, California 92521 USA
| | - Elizabeth A. Savory
- Department of Botany and Plant Pathology, Cordley Hall, 2701 SW Campus Way, Oregon State University, Corvallis, Oregon 97331 USA
| | - Jeff H. Chang
- Department of Botany and Plant Pathology, Cordley Hall, 2701 SW Campus Way, Oregon State University, Corvallis, Oregon 97331 USA
| | - Joel L. Sachs
- Department of Evolution, Ecology, and Organismal Biology, 2710 Life Sciences Building, University of California, Riverside, California 92521 USA
- Department of Botany and Plant Sciences, 2142 Batchelor Hall, University of California, Riverside, California 92521 USA
- Institute for Integrative Genome Biology, 5406 Boyce Hall, University of California, Riverside, California 92521 USA
| |
Collapse
|
31
|
Westhoek A, Field E, Rehling F, Mulley G, Webb I, Poole PS, Turnbull LA. Policing the legume-Rhizobium symbiosis: a critical test of partner choice. Sci Rep 2017; 7:1419. [PMID: 28469244 PMCID: PMC5431162 DOI: 10.1038/s41598-017-01634-2] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 04/03/2017] [Indexed: 11/29/2022] Open
Abstract
In legume-Rhizobium symbioses, specialised soil bacteria fix atmospheric nitrogen in return for carbon. However, ineffective strains can arise, making discrimination essential. Discrimination can occur via partner choice, where legumes prevent ineffective strains from entering, or via sanctioning, where plants provide fewer resources. Several studies have inferred that legumes exercise partner choice, but the rhizobia compared were not otherwise isogenic. To test when and how plants discriminate ineffective strains we developed sets of fixing and non-fixing strains that differed only in the expression of nifH - essential for nitrogen fixation - and could be visualised using marker genes. We show that the plant is unable to select against the non-fixing strain at the point of entry, but that non-fixing nodules are sanctioned. We also used the technique to characterise mixed nodules (containing both a fixing and a non-fixing strain), whose frequency could be predicted using a simple diffusion model. We discuss that sanctioning is likely to evolve in preference to partner choice in any symbiosis where partner quality cannot be adequately assessed until goods or services are actively exchanged.
Collapse
Affiliation(s)
- Annet Westhoek
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK
- Systems Biology Doctoral Training Centre, University of Oxford, Oxford, OX1 3RQ, UK
| | - Elsa Field
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK
| | - Finn Rehling
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK
- Department of Ecology, Philipps-University Marburg, Marburg, D-35043, Germany
| | - Geraldine Mulley
- School of Biological Sciences, University of Reading, Reading, RG6 6AJ, UK
| | - Isabel Webb
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK
| | - Philip S Poole
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK.
| | - Lindsay A Turnbull
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK.
| |
Collapse
|
32
|
Batstone RT, Dutton EM, Wang D, Yang M, Frederickson ME. The evolution of symbiont preference traits in the model legume Medicago truncatula. THE NEW PHYTOLOGIST 2017; 213:1850-1861. [PMID: 27864973 DOI: 10.1111/nph.14308] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Accepted: 09/23/2016] [Indexed: 05/25/2023]
Abstract
Many hosts preferentially associate with or reward better symbionts, but how these symbiont preference traits evolve is an open question. Legumes often form more nodules with or provide more resources to rhizobia that fix more nitrogen (N), but they also acquire N from soil via root foraging. It is unclear whether root responses to abiotically and symbiotically derived N evolve independently. Here, we measured root foraging and both preferential allocation of root resources to and preferential association with an effective vs an ineffective N-fixing Ensifer meliloti strain in 35 inbred lines of the model legume Medicago truncatula. We found that M. truncatula is an efficient root forager and forms more nodules with the effective rhizobium; root biomass increases with the number of effective, but not ineffective, nodules, indicating preferential allocation to roots harbouring effective rhizobia; root foraging is not genetically correlated with either preferential allocation or association; and selection favours plant genotypes that form more effective nodules. Root foraging and symbiont preference traits appear to be genetically uncoupled in M. truncatula. Rather than evolving to exclude ineffective partners, our results suggest that preference traits probably evolve to take better advantage of effective symbionts.
Collapse
Affiliation(s)
- Rebecca T Batstone
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Emily M Dutton
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Donglin Wang
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Molly Yang
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Megan E Frederickson
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| |
Collapse
|
33
|
Klinger CR, Lau JA, Heath KD. Ecological genomics of mutualism decline in nitrogen-fixing bacteria. Proc Biol Sci 2016; 283:20152563. [PMID: 26962142 DOI: 10.1098/rspb.2015.2563] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Anthropogenic changes can influence mutualism evolution; however, the genomic regions underpinning mutualism that are most affected by environmental change are generally unknown, even in well-studied model mutualisms like the interaction between legumes and their nitrogen (N)-fixing rhizobia. Such genomic information can shed light on the agents and targets of selection maintaining cooperation in nature. We recently demonstrated that N-fertilization has caused an evolutionary decline in mutualistic partner quality in the rhizobia that form symbiosis with clover. Here, population genomic analyses of N-fertilized versus control rhizobium populations indicate that evolutionary differentiation at a key symbiosis gene region on the symbiotic plasmid (pSym) contributes to partner quality decline. Moreover, patterns of genetic variation at selected loci were consistent with recent positive selection within N-fertilized environments, suggesting that N-rich environments might select for less beneficial rhizobia. By studying the molecular population genomics of a natural bacterial population within a long-term ecological field experiment, we find that: (i) the N environment is indeed a potent selective force mediating mutualism evolution in this symbiosis, (ii) natural variation in rhizobium partner quality is mediated in part by key symbiosis genes on the symbiotic plasmid, and (iii) differentiation at selected genes occurred in the context of otherwise recombining genomes, resembling eukaryotic models of adaptation.
Collapse
Affiliation(s)
- Christie R Klinger
- Department of Plant Biology, University of Illinois Urbana-Champaign, 505 South Goodwin Avenue, Urbana, IL 61801, USA
| | - Jennifer A Lau
- W.K. Kellogg Biological Station and Department of Plant Biology, Michigan State University, East Lansing, MI, USA
| | - Katy D Heath
- Department of Plant Biology, University of Illinois Urbana-Champaign, 505 South Goodwin Avenue, Urbana, IL 61801, USA
| |
Collapse
|
34
|
Yoder JB. Understanding the coevolutionary dynamics of mutualism with population genomics. AMERICAN JOURNAL OF BOTANY 2016; 103:1742-1752. [PMID: 27756732 DOI: 10.3732/ajb.1600154] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Accepted: 09/06/2016] [Indexed: 06/06/2023]
Abstract
Decades of research on the evolution of mutualism has generated a wealth of possible ways whereby mutually beneficial interactions between species persist in spite of the apparent advantages to individuals that accept the benefits of mutualism without reciprocating - but identifying how any particular empirical system is stabilized against cheating remains challenging. Different hypothesized models of mutualism stability predict different forms of coevolutionary selection, and emerging high-throughput sequencing methods allow examination of the selective histories of mutualism genes and, thereby, the form of selection acting on those genes. Here, I review the evolutionary theory of mutualism stability and identify how differing models make contrasting predictions for the population genomic diversity and geographic differentiation of mutualism-related genes. As an example of the possibilities offered by genomic data, I analyze genes with roles in the symbiosis of Medicago truncatula and nitrogen-fixing rhizobial bacteria, the first classic mutualism in which extensive genomic resources have been developed for both partners. Medicago truncatula symbiosis genes, as a group, differ from the rest of the genome, but they vary in the form of selection indicated by their diversity and differentiation - some show signs of selection expected from roles in sanctioning noncooperative symbionts, while others show evidence of balancing selection expected from coevolution with symbiont signaling factors. I then assess the current state of development for similar resources in other mutualistic interactions and look ahead to identify ways in which modern sequencing technology can best inform our understanding of mutualists and mutualism.
Collapse
Affiliation(s)
- Jeremy B Yoder
- Department of Forest and Conservation Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4 Canada
| |
Collapse
|
35
|
Yoder JB, Leebens-Mack J. The evolutionary ecology of "mutual services" in the 21st century. AMERICAN JOURNAL OF BOTANY 2016; 103:1712-1716. [PMID: 27793857 DOI: 10.3732/ajb.1600367] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 10/13/2016] [Indexed: 06/06/2023]
Affiliation(s)
- Jeremy B Yoder
- Department of Forest and Conservation Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4 Canada
| | - James Leebens-Mack
- Department of Plant Biology, University of Georgia, Athens, Georgia 30602-7271 USA
| |
Collapse
|
36
|
Grillo MA, Stinchcombe JR, Heath KD. Nitrogen addition does not influence pre-infection partner choice in the legume-rhizobium symbiosis. AMERICAN JOURNAL OF BOTANY 2016; 103:1763-1770. [PMID: 27671532 DOI: 10.3732/ajb.1600090] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Accepted: 08/09/2016] [Indexed: 05/26/2023]
Abstract
PREMISE OF THE STUDY Resource mutualisms such as the symbiosis between legumes and nitrogen-fixing rhizobia are context dependent and are sensitive to various aspects of the environment, including nitrogen (N) addition. Mutualist hosts such as legumes are also thought to use mechanisms such as partner choice to discriminate among potential symbionts that vary in partner quality (fitness benefits conferred to hosts) and thus impose selection on rhizobium populations. Together, context dependency and partner choice might help explain why the legume-rhizobium mutualism responds evolutionarily to N addition, since plant-mediated selection that shifts in response to N might be expected to favor different rhizobium strains in different N environments. METHODS We test for the influence of context dependency on partner choice in the model legume, Medicago truncatula, using a factorial experiments with three plant families across three N levels with a mixed inoculation of three rhizobia strains. KEY RESULTS Neither the relative frequencies of rhizobium strains occupying host nodules, nor the size of those nodules, differed in response to N level. CONCLUSIONS Despite the lack of context dependence, plant genotypes respond very differently to mixed populations of rhizobia, suggesting that these traits are genetically variable and thus could evolve in response to longer-term increases in N.
Collapse
Affiliation(s)
- Michael A Grillo
- University of Illinois, Department of Plant Biology, Urbana, Illinois 61801, USA
| | - John R Stinchcombe
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B2
| | - Katy D Heath
- University of Illinois, Department of Plant Biology, Urbana, Illinois 61801, USA
| |
Collapse
|
37
|
Nonnodulating Bradyrhizobium spp. Modulate the Benefits of Legume-Rhizobium Mutualism. Appl Environ Microbiol 2016; 82:5259-68. [PMID: 27316960 DOI: 10.1128/aem.01116-16] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Accepted: 06/13/2016] [Indexed: 12/21/2022] Open
Abstract
UNLABELLED Rhizobia are best known for nodulating legume roots and fixing atmospheric nitrogen for the host in exchange for photosynthates. However, the majority of the diverse strains of rhizobia do not form nodules on legumes, often because they lack key loci that are needed to induce nodulation. Nonnodulating rhizobia are robust heterotrophs that can persist in bulk soil, thrive in the rhizosphere, or colonize roots as endophytes, but their role in the legume-rhizobium mutualism remains unclear. Here, we investigated the effects of nonnodulating strains on the native Acmispon-Bradyrhizobium mutualism. To examine the effects on both host performance and symbiont fitness, we performed clonal inoculations of diverse nonnodulating Bradyrhizobium strains on Acmispon strigosus hosts and also coinoculated hosts with mixtures of sympatric nodulating and nonnodulating strains. In isolation, nonnodulating Bradyrhizobium strains did not affect plant performance. In most cases, coinoculation of nodulating and nonnodulating strains reduced host performance compared to that of hosts inoculated with only a symbiotic strain. However, coinoculation increased host performance only under one extreme experimental treatment. Nearly all estimates of nodulating strain fitness were reduced in the presence of nonnodulating strains. We discovered that nonnodulating strains were consistently capable of coinfecting legume nodules in the presence of nodulating strains but that the fitness effects of coinfection for hosts and symbionts were negligible. Our data suggest that nonnodulating strains most often attenuate the Acmispon-Bradyrhizobium mutualism and that this occurs via competitive interactions at the root-soil interface as opposed to in planta IMPORTANCE Rhizobia are soil bacteria best known for their capacity to form root nodules on legume plants and enhance plant growth through nitrogen fixation. Yet, most rhizobia in soil do not have this capacity, and their effects on this symbiosis are poorly understood. We investigated the effects of diverse nonnodulating rhizobia on a native legume-rhizobium symbiosis. Nonnodulating strains did not affect plant growth in isolation. However, compared to inoculations with symbiotic rhizobia, coinoculations of symbiotic and nonnodulating strains often reduced plant and symbiont fitness. Coinoculation increased host performance only under one extreme treatment. Nonnodulating strains also invaded nodule interiors in the presence of nodulating strains, but this did not affect the fitness of either partner. Our data suggest that nonnodulating strains may be important competitors at the root-soil interface and that their capacity to attenuate this symbiosis should be considered in efforts to use rhizobia as biofertilizers.
Collapse
|
38
|
Estrela S, Kerr B, Morris JJ. Transitions in individuality through symbiosis. Curr Opin Microbiol 2016; 31:191-198. [DOI: 10.1016/j.mib.2016.04.007] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Revised: 04/07/2016] [Accepted: 04/08/2016] [Indexed: 11/29/2022]
|
39
|
Hollowell AC, Regus JU, Turissini D, Gano-Cohen KA, Bantay R, Bernardo A, Moore D, Pham J, Sachs JL. Metapopulation dominance and genomic-island acquisition of Bradyrhizobium with superior catabolic capabilities. Proc Biol Sci 2016; 283:20160496. [PMID: 27122562 PMCID: PMC4855393 DOI: 10.1098/rspb.2016.0496] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Accepted: 04/04/2016] [Indexed: 01/05/2023] Open
Abstract
Root nodule-forming rhizobia exhibit a bipartite lifestyle, replicating in soil and also within plant cells where they fix nitrogen for legume hosts. Host control models posit that legume hosts act as a predominant selective force on rhizobia, but few studies have examined rhizobial fitness in natural populations. Here, we genotyped and phenotyped Bradyrhizobium isolates across more than 800 km of the native Acmispon strigosus host range. We sequenced chromosomal genes expressed under free-living conditions and accessory symbiosis loci expressed in planta and encoded on an integrated 'symbiosis island' (SI). We uncovered a massive clonal expansion restricted to the Bradyrhizobium chromosome, with a single chromosomal haplotype dominating populations, ranging more than 700 km, and acquiring 42 divergent SI haplotypes, none of which were spatially widespread. For focal genotypes, we quantified utilization of 190 sole-carbon sources relevant to soil fitness. Chromosomal haplotypes that were both widespread and dominant exhibited superior growth on diverse carbon sources, whereas these patterns were not mirrored among SI haplotypes. Abundance, spatial range and catabolic superiority of chromosomal, but not symbiosis genotypes suggests that fitness in the soil environment, rather than symbiosis with hosts, might be the key driver of Bradyrhizobium dominance.
Collapse
Affiliation(s)
- Amanda C Hollowell
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - John U Regus
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - David Turissini
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA
| | | | - Roxanne Bantay
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - Andrew Bernardo
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - Devora Moore
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - Jonathan Pham
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - Joel L Sachs
- Department of Biology, University of California, Riverside, CA 92521, USA Institute for Integrative Genome Biology, University of California, Riverside, CA 92521, USA
| |
Collapse
|
40
|
Hollowell AC, Regus JU, Gano KA, Bantay R, Centeno D, Pham J, Lyu JY, Moore D, Bernardo A, Lopez G, Patil A, Patel S, Lii Y, Sachs JL. Epidemic Spread of Symbiotic and Non-Symbiotic Bradyrhizobium Genotypes Across California. MICROBIAL ECOLOGY 2016; 71:700-710. [PMID: 26467244 DOI: 10.1007/s00248-015-0685-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Accepted: 09/28/2015] [Indexed: 06/05/2023]
Abstract
The patterns and drivers of bacterial strain dominance remain poorly understood in natural populations. Here, we cultured 1292 Bradyrhizobium isolates from symbiotic root nodules and the soil root interface of the host plant Acmispon strigosus across a >840-km transect in California. To investigate epidemiology and the potential role of accessory loci as epidemic drivers, isolates were genotyped at two chromosomal loci and were assayed for presence or absence of accessory "symbiosis island" loci that encode capacity to form nodules on hosts. We found that Bradyrhizobium populations were very diverse but dominated by few haplotypes-with a single "epidemic" haplotype constituting nearly 30 % of collected isolates and spreading nearly statewide. In many Bradyrhizobium lineages, we inferred presence and absence of the symbiosis island suggesting recurrent evolutionary gain and or loss of symbiotic capacity. We did not find statistical phylogenetic evidence that the symbiosis island acquisition promotes strain dominance and both symbiotic and non-symbiotic strains exhibited population dominance and spatial spread. Our dataset reveals that a strikingly few Bradyrhizobium genotypes can rapidly spread to dominate a landscape and suggests that these epidemics are not driven by the acquisition of accessory loci as occurs in key human pathogens.
Collapse
Affiliation(s)
- A C Hollowell
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - J U Regus
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - K A Gano
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - R Bantay
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - D Centeno
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - J Pham
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - J Y Lyu
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - D Moore
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - A Bernardo
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - G Lopez
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - A Patil
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - S Patel
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - Y Lii
- Department of Biology, University of California, Riverside, CA, 92521, USA
| | - J L Sachs
- Department of Biology, University of California, Riverside, CA, 92521, USA.
- Institute for Integrative Genome Biology, University of California, Riverside, CA, 95616, USA.
| |
Collapse
|
41
|
Morran LT, Penley MJ, Byrd VS, Meyer AJ, O'Sullivan TS, Bashey F, Goodrich-Blair H, Lively CM. Nematode-bacteria mutualism: Selection within the mutualism supersedes selection outside of the mutualism. Evolution 2016; 70:687-95. [PMID: 26867502 DOI: 10.1111/evo.12878] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2015] [Accepted: 01/25/2016] [Indexed: 01/06/2023]
Abstract
The coevolution of interacting species can lead to codependent mutualists. Little is known about the effect of selection on partners within verses apart from the association. Here, we determined the effect of selection on bacteria (Xenorhabdus nematophila) both within and apart from its mutualistic partner (a nematode, Steinernema carpocapsae). In nature, the two species cooperatively infect and kill arthropods. We passaged the bacteria either together with (M+), or isolated from (M-), nematodes under two different selection regimes: random selection (S-) and selection for increased virulence against arthropod hosts (S+). We found that the isolated bacteria evolved greater virulence under selection for greater virulence (M-S+) than under random selection (M-S-). In addition, the response to selection in the isolated bacteria (M-S+) caused a breakdown of the mutualism following reintroduction to the nematode. Finally, selection for greater virulence did not alter the evolutionary trajectories of bacteria passaged within the mutualism (M+S+ = M+S-), indicating that selection for the maintenance of the mutualism was stronger than selection for increased virulence. The results show that selection on isolated mutualists can rapidly breakdown beneficial interactions between species, but that selection within a mutualism can supersede external selection, potentially generating codependence over time.
Collapse
Affiliation(s)
- Levi T Morran
- Department of Biology, Indiana University, 1001 E. Third St., Bloomington, Indiana, 47405. .,Department of Biology, Emory University, 1510 Clifton Rd. NE, Atlanta, Georgia, 30322.
| | - McKenna J Penley
- Department of Biology, Indiana University, 1001 E. Third St., Bloomington, Indiana, 47405.,Department of Biology, Emory University, 1510 Clifton Rd. NE, Atlanta, Georgia, 30322
| | - Victoria S Byrd
- Department of Biology, Indiana University, 1001 E. Third St., Bloomington, Indiana, 47405
| | - Andrew J Meyer
- Department of Biology, Indiana University, 1001 E. Third St., Bloomington, Indiana, 47405
| | - Timothy S O'Sullivan
- Department of Biology, Indiana University, 1001 E. Third St., Bloomington, Indiana, 47405.,Department of Biology, Emory University, 1510 Clifton Rd. NE, Atlanta, Georgia, 30322
| | - Farrah Bashey
- Department of Biology, Indiana University, 1001 E. Third St., Bloomington, Indiana, 47405
| | - Heidi Goodrich-Blair
- Department of Bacteriology, University of Wisconsin-Madison, 1550 Linden Dr. Madison, Madison, Wisconsin, 53706
| | - Curtis M Lively
- Department of Biology, Indiana University, 1001 E. Third St., Bloomington, Indiana, 47405
| |
Collapse
|
42
|
Gordon BR, Klinger CR, Weese DJ, Lau JA, Burke PV, Dentinger BTM, Heath KD. Decoupled genomic elements and the evolution of partner quality in nitrogen-fixing rhizobia. Ecol Evol 2016; 6:1317-27. [PMID: 27087920 PMCID: PMC4775534 DOI: 10.1002/ece3.1953] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Revised: 12/14/2015] [Accepted: 12/15/2015] [Indexed: 01/24/2023] Open
Abstract
Understanding how mutualisms evolve in response to a changing environment will be critical for predicting the long-term impacts of global changes, such as increased N (nitrogen) deposition. Bacterial mutualists in particular might evolve quickly, thanks to short generation times and the potential for independent evolution of plasmids through recombination and/or HGT (horizontal gene transfer). In a previous work using the legume/rhizobia mutualism, we demonstrated that long-term nitrogen fertilization caused the evolution of less-mutualistic rhizobia. Here, we use our 63 previously isolated rhizobium strains in comparative phylogenetic and quantitative genetic analyses to determine the degree to which variation in partner quality is attributable to phylogenetic relationships among strains versus recent genetic changes in response to N fertilization. We find evidence of distinct evolutionary relationships between chromosomal and pSym genes, and broad similarity between pSym genes. We also find that nifD has a unique evolutionary history that explains much of the variation in partner quality, and suggest MoFe subunit interaction sites in the evolution of less-mutualistic rhizobia. These results provide insight into the mechanisms behind the evolutionary response of rhizobia to long-term N fertilization, and we discuss the implications of our results for the evolution of the mutualism.
Collapse
Affiliation(s)
- Benjamin R. Gordon
- Department of Plant BiologyUniversity of Illinois Urbana‐Champaign505 S. Goodwin Ave.UrbanaIllinois61801
| | - Christie R. Klinger
- Department of Plant BiologyUniversity of Illinois Urbana‐Champaign505 S. Goodwin Ave.UrbanaIllinois61801
| | - Dylan J. Weese
- Department of BiologySt. Ambrose University518 West Locust StDavenportIowa52803
| | - Jennifer A. Lau
- Kellogg Biological Station and Department of Plant BiologyMichigan State University3700 E. Gull Lake DriveHickory CornersMichigan49060
| | - Patricia V. Burke
- Department of Plant BiologyUniversity of Illinois Urbana‐Champaign505 S. Goodwin Ave.UrbanaIllinois61801
| | | | - Katy D. Heath
- Department of Plant BiologyUniversity of Illinois Urbana‐Champaign505 S. Goodwin Ave.UrbanaIllinois61801
| |
Collapse
|
43
|
Miranda-Sánchez F, Rivera J, Vinuesa P. Diversity patterns ofRhizobiaceaecommunities inhabiting soils, root surfaces and nodules reveal a strong selection of rhizobial partners by legumes. Environ Microbiol 2015; 18:2375-91. [DOI: 10.1111/1462-2920.13061] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Accepted: 09/17/2015] [Indexed: 10/23/2022]
Affiliation(s)
- Fabiola Miranda-Sánchez
- Programa de Ingeniería Genómica; Centro de Ciencias Genómicas; Universidad Nacional Autónoma de México; Cuernavaca Morelos 62210 Mexico
| | - Javier Rivera
- Programa de Ingeniería Genómica; Centro de Ciencias Genómicas; Universidad Nacional Autónoma de México; Cuernavaca Morelos 62210 Mexico
| | - Pablo Vinuesa
- Programa de Ingeniería Genómica; Centro de Ciencias Genómicas; Universidad Nacional Autónoma de México; Cuernavaca Morelos 62210 Mexico
| |
Collapse
|
44
|
Simonsen AK, Stinchcombe JR. Standing genetic variation in host preference for mutualist microbial symbionts. Proc Biol Sci 2015; 281:rspb.2014.2036. [PMID: 25355477 DOI: 10.1098/rspb.2014.2036] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Many models of mutualisms show that mutualisms are unstable if hosts lack mechanisms enabling preferential associations with mutualistic symbiotic partners over exploitative partners. Despite the theoretical importance of mutualism-stabilizing mechanisms, we have little empirical evidence to infer their evolutionary dynamics in response to exploitation by non-beneficial partners. Using a model mutualism-the interaction between legumes and nitrogen-fixing soil symbionts-we tested for quantitative genetic variation in plant responses to mutualistic and exploitative symbiotic rhizobia in controlled greenhouse conditions. We found significant broad-sense heritability in a legume host's preferential association with mutualistic over exploitative symbionts and selection to reduce frequency of associations with exploitative partners. We failed to detect evidence that selection will favour the loss of mutualism-stabilizing mechanisms in the absence of exploitation, as we found no evidence for a fitness cost to the host trait or indirect selection on genetically correlated traits. Our results show that genetic variation in the ability to preferentially reduce associations with an exploitative partner exists within mutualisms and is under selection, indicating that micro-evolutionary responses in mutualism-stabilizing traits in the face of rapidly evolving mutualistic and exploitative symbiotic bacteria can occur in natural host populations.
Collapse
Affiliation(s)
- Anna K Simonsen
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Canada M5S 3B2
| | - John R Stinchcombe
- Department of Ecology and Evolutionary Biology & Centre for the Analysis of Genome Evolution and Function, University of Toronto, 25 Willcocks Street, Toronto, Canada M5S 3B2
| |
Collapse
|
45
|
Bever JD. Preferential allocation, physio-evolutionary feedbacks, and the stability and environmental patterns of mutualism between plants and their root symbionts. THE NEW PHYTOLOGIST 2015; 205:1503-1514. [PMID: 25561086 DOI: 10.1111/nph.13239] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Accepted: 11/15/2014] [Indexed: 05/09/2023]
Abstract
The common occurrence of mutualistic interactions between plants and root symbionts is problematic. As the delivery of benefit to hosts involves costs to symbionts, symbionts that provide reduced benefit to their host are expected to increase in frequency. Plants have been shown to allocate preferentially to the most efficient symbiont and this preferential allocation may stabilize the mutualism. I construct a general model of the interactive feedbacks of host preferential allocation and the dynamics of root symbiont populations to evaluate the stability of nutritional mutualisms. Preferential allocation can promote the evolution of mutualism even when the cost to the symbiont is very large. Moreover, the physiological plasticity of preferential allocation likely leads to coexistence of beneficial and nonbeneficial symbionts. For arbuscular mycorrhizal fungi, which facilitate plant uptake of phosphorus (P), the model predicts greater P transfer from these fungi per unit carbon invested with decreasing concentrations of soil P and with increasing concentrations of atmospheric CO2 , patterns that have been observed in laboratory and field studies. This framework connects physiological plasticity in plant allocation to population processes that determine mutualism stability and, as such, represents a significant step in understanding the stability and environmental patterns in mutualism.
Collapse
Affiliation(s)
- James D Bever
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
| |
Collapse
|
46
|
Regus JU, Gano KA, Hollowell AC, Sofish V, Sachs JL. Lotus
hosts delimit the mutualism-parasitism continuum of Bradyrhizobium. J Evol Biol 2015; 28:447-56. [DOI: 10.1111/jeb.12579] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2014] [Revised: 10/15/2014] [Accepted: 12/22/2014] [Indexed: 01/24/2023]
Affiliation(s)
- J. U. Regus
- Department of Biology; University of California; Riverside CA USA
| | - K. A. Gano
- Department of Biology; University of California; Riverside CA USA
| | - A. C. Hollowell
- Department of Biology; University of California; Riverside CA USA
| | - V. Sofish
- Department of Biology; University of California; Riverside CA USA
| | - J. L. Sachs
- Department of Biology; University of California; Riverside CA USA
- Institute for Integrative Genome Biology; University of California; Riverside CA USA
| |
Collapse
|
47
|
Behm JE, Geurts R, Kiers ET. Parasponia: a novel system for studying mutualism stability. TRENDS IN PLANT SCIENCE 2014; 19:757-63. [PMID: 25239777 DOI: 10.1016/j.tplants.2014.08.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Revised: 08/21/2014] [Accepted: 08/23/2014] [Indexed: 05/05/2023]
Abstract
Understanding how mutualistic interactions are stabilized in the presence of cheaters is a major question in evolutionary biology. The legume-rhizobia mutualism has become a model system for studying how plants control cheating partners. However, the generality and evolutionary origins of these control mechanisms are intensely debated. In this Opinion article, we argue that a novel system--the Parasponia-rhizobia mutualism--will significantly advance research in mutualism stability. Parasponia is the only non-legume lineage to have evolved a rhizobial symbiosis, which provides an evolutionary replicate to test how rhizobial exploitation is controlled. Evidence also suggests that this symbiosis is young. This allows studies at an earlier evolutionary stage in mutualisms, so the origin of control mechanisms can be better understood.
Collapse
Affiliation(s)
- Jocelyn E Behm
- Department of Ecological Science, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, de Boelelaan 1085, 1081HV Amsterdam, The Netherlands.
| | - Rene Geurts
- Department of Plant Science, Laboratory of Molecular Biology, Wageningen University, Drovendaalsesteeg 1, 6709PB Wageningen, The Netherlands
| | - E Toby Kiers
- Department of Ecological Science, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, de Boelelaan 1085, 1081HV Amsterdam, The Netherlands
| |
Collapse
|
48
|
Wyatt GAK, Kiers ET, Gardner A, West SA. A BIOLOGICAL MARKET ANALYSIS OF THE PLANT-MYCORRHIZAL SYMBIOSIS. Evolution 2014; 68:2603-18. [DOI: 10.1111/evo.12466] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Accepted: 05/27/2014] [Indexed: 12/21/2022]
Affiliation(s)
| | - E. Toby Kiers
- Institute of Ecological Sciences; Faculty of Earth and Life Sciences; Vrije Universiteit; De Boelelaan 1085, 1081 HV Amsterdam The Netherlands
| | - Andy Gardner
- School of Biology; University of St Andrews; Dyers Brae, St Andrews KY16 9 United Kingdom
| | - Stuart A. West
- Department of Zoology; University of Oxford; Oxford OX1 3PS United Kingdom
| |
Collapse
|