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Rivest S, Forrest JRK. Do flower-colonizing microbes influence floral evolution? A test with fast-cycling Brassica. J Evol Biol 2024; 37:935-946. [PMID: 38902913 DOI: 10.1093/jeb/voae078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2023] [Revised: 05/13/2024] [Accepted: 06/20/2024] [Indexed: 06/22/2024]
Abstract
Pollinators are thought to be the main drivers of floral evolution. Flowers are also colonized by abundant communities of microbes that can affect the interaction between plants and their pollinators. Very little is known, however, about how flower-colonizing microbes influence floral evolution. Here we performed a 6-generation experimental evolution study using fast-cycling Brassica rapa, in which we factorially manipulated the presence of pollinators and flower microbes to determine how pollinators and microbes interact in driving floral evolution. We measured the evolution of 6 morphological traits, as well as the plant mating system and flower attractiveness. Only one of the 6 traits (flower number) evolved in response to pollinators, while microbes did not drive the evolution of any trait, nor did they interact with pollinators in driving the evolution of morphological traits. Moreover, we did not find evidence that pollinators or microbes affected the evolution of flower attractiveness to pollinators. However, we found an interactive effect of pollinators and microbes on the evolution of autonomous selfing, a trait that is expected to evolve in response to pollinator limitations. Overall, we found only weak evidence that microbes mediate floral evolution. However, our ability to detect an interactive effect of pollinators and microbes might have been limited by weak pollinator-mediated selection in our experimental setting. Our results contrast with previous (similar) experimental evolution studies, highlighting the susceptibility of such experiments to drift and to experimental artefacts.
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Affiliation(s)
- Sébastien Rivest
- Department of Biology, University of Ottawa, Ottawa, ON K1N 6N5, Canada
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2
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Tiusanen M, Becker-Scarpitta A, Wirta H. Distinct Communities and Differing Dispersal Routes in Bacteria and Fungi of Honey Bees, Honey, and Flowers. MICROBIAL ECOLOGY 2024; 87:100. [PMID: 39080099 PMCID: PMC11289361 DOI: 10.1007/s00248-024-02413-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2024] [Accepted: 07/16/2024] [Indexed: 08/02/2024]
Abstract
Microbiota, the communities of microbes on and in organisms or organic matter, are essential for the functioning of ecosystems. How microbes are shared and transmitted delineates the formation of a microbiota. As pollinators forage, they offer a route to transfer microbes among the flowering plants, themselves, and their nests. To assess how the two components of the microbiota, bacteria and fungi, in pollination communities are shared and transferred, we focused on the honey bee Apis mellifera and collected honey bee, honey (representing the hive microbiota), and flower samples three times during the summer in Finland. We identified the bacteria and fungi by DNA metabarcoding. To determine the impact of honey bees' flower choices on the honey bee and hive microbiota, we identified also plant DNA in honey. The bacterial communities of honey bees, honey, and flowers all differ greatly from each other, while the fungal communities of honey bees and honey are very similar, yet different from flowers. The time of the summer and the sampling area influence all these microbiota. For flowers, the plant identity impacts both bacterial and fungal communities' composition the most. For the dispersal pathways of bacteria to honey bees, they are acquired directly from the honey and indirectly from flowers through the honey, while fungi are directly transmitted to honey bees from flowers. Overall, the distinctiveness of the microbiota of honey bees, honey, and the surrounding flowers suggests the sharing of microbes among them occurs but plays a minor role for the established microbiota.
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Affiliation(s)
- Mikko Tiusanen
- Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland
- Department of Environmental Systems Science, Eidgenössische Technische Hochschule Zürich (ETH Zürich), Zurich, Switzerland
| | - Antoine Becker-Scarpitta
- Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland
- UMR PVBMT, CIRAD, Saint Pierre, 97410, La Réunion, France
| | - Helena Wirta
- Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland.
- Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
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3
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Rivest S, Lee ST, Cook D, Forrest JRK. Consequences of pollen defense compounds for pollinators and antagonists in a pollen-rewarding plant. Ecology 2024; 105:e4306. [PMID: 38590050 DOI: 10.1002/ecy.4306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Revised: 01/09/2024] [Accepted: 02/19/2024] [Indexed: 04/10/2024]
Abstract
Plants produce an array of defensive compounds with toxic or deterrent effects on insect herbivores. Pollen can contain relatively high concentrations of such defense compounds, but the causes and consequences of this enigmatic phenomenon remain mostly unknown. These compounds could potentially protect pollen against antagonists but could also reduce flower attractiveness to pollinators. We combined field observations of the pollen-rewarding Lupinus argenteus with chemical analysis and laboratory assays to test three hypotheses for the presence of pollen defense compounds: (1) these compounds are the result of spillover from adjacent tissues, (2) they protect against pollen thieves, and (3) they act as antimicrobial compounds. We also tested whether pollen defense compounds affect pollinator behavior. We found a positive relationship between alkaloid concentrations in pollen and petals, supporting the idea that pollen defense compounds partly originate from spillover. However, pollen and petals exhibited quantitatively (but not qualitatively) distinct alkaloid profiles, suggesting that plants can adjust pollen alkaloid composition independently from that of adjacent tissues. We found no relationship between pollen alkaloid concentration and the abundance of pollen thieves in Lupinus flowers. However, pollen alkaloids were negatively associated with bacterial abundance. Finally, plants with more alkaloids in their pollen received more pollinator visits, but these visits were shorter, resulting in no change in the overall number of flowers visited. We propose that pollen defense compounds are partly the result of spillover from other tissues, while they also play an antimicrobial role. The absence of negative effects of these compounds on pollinator visitation likely allows their maintenance in pollen at relatively high concentrations. Taken together, our results suggest that pollen alkaloids affect and are mediated by the interplay of multiple interactions.
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Affiliation(s)
- Sébastien Rivest
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
- Rocky Mountain Biological Laboratory, Crested Butte, Colorado, USA
| | - Stephen T Lee
- USDA ARS Poisonous Plant Research Laboratory, Logan, Utah, USA
| | - Daniel Cook
- USDA ARS Poisonous Plant Research Laboratory, Logan, Utah, USA
| | - Jessica R K Forrest
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
- Rocky Mountain Biological Laboratory, Crested Butte, Colorado, USA
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4
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Christian N, Perlin MH. Plant-endophyte communication: Scaling from molecular mechanisms to ecological outcomes. Mycologia 2024; 116:227-250. [PMID: 38380970 DOI: 10.1080/00275514.2023.2299658] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 12/22/2023] [Indexed: 02/22/2024]
Abstract
Diverse communities of fungal endophytes reside in plant tissues, where they affect and are affected by plant physiology and ecology. For these intimate interactions to form and persist, endophytes and their host plants engage in intricate systems of communication. The conversation between fungal endophytes and plant hosts ultimately dictates endophyte community composition and function and has cascading effects on plant health and plant interactions. In this review, we synthesize our current knowledge on the mechanisms and strategies of communication used by endophytic fungi and their plant hosts. We discuss the molecular mechanisms of communication that lead to organ specificity of endophytic communities and distinguish endophytes, pathogens, and saprotrophs. We conclude by offering emerging perspectives on the relevance of plant-endophyte communication to microbial community ecology and plant health and function.
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Affiliation(s)
- Natalie Christian
- Department of Biology, University of Louisville, Louisville, Kentucky 40292
| | - Michael H Perlin
- Department of Biology, University of Louisville, Louisville, Kentucky 40292
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5
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Cardinale M, Schnell S. Is the plant microbiome transmitted from pollen to seeds? Front Microbiol 2024; 15:1343795. [PMID: 38414764 PMCID: PMC10897013 DOI: 10.3389/fmicb.2024.1343795] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2023] [Accepted: 01/29/2024] [Indexed: 02/29/2024] Open
Affiliation(s)
- Massimiliano Cardinale
- Department of Biological and Environmental Sciences and Technologies, University of Salento, Lecce, Italy
| | - Sylvia Schnell
- Institute of Applied Microbiology, Justus-Liebig-University Giessen, Giessen, Germany
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6
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Álvarez-Pérez S, Lievens B, de Vega C. Floral nectar and honeydew microbial diversity and their role in biocontrol of insect pests and pollination. CURRENT OPINION IN INSECT SCIENCE 2024; 61:101138. [PMID: 37931689 DOI: 10.1016/j.cois.2023.101138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2023] [Revised: 10/29/2023] [Accepted: 10/30/2023] [Indexed: 11/08/2023]
Abstract
Sugar-rich plant-related secretions, such as floral nectar and honeydew, that are commonly used as nutrient sources by insects and other animals, are also the ecological niche for diverse microbial communities. Recent research has highlighted the great potential of nectar and honeydew microbiomes in biological pest control and improved pollination, but the exploitation of these microbiomes requires a deep understanding of their community dynamics and plant-microbe-insect interactions. Additionally, the successful application of microbes in crop fields is conditioned by diverse ecological, legal, and ethical challenges that should be taken into account. In this article, we provide an overview of the nectar and honeydew microbiomes and discuss their potential applications in sustainable agricultural practices.
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Affiliation(s)
- Sergio Álvarez-Pérez
- Department of Animal Health, Complutense University of Madrid, 28040 Madrid, Spain.
| | - Bart Lievens
- Laboratory for Process Microbial Ecology and Bioinspirational Management (PME&BIM), Department of Microbial and Molecular Systems, KU Leuven, B-3001 Heverlee, Belgium
| | - Clara de Vega
- Departamento de Biología Vegetal y Ecología, Universidad de Sevilla, 41012 Sevilla, Spain
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7
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Steffan SA, Dharampal PS, Kueneman JG, Keller A, Argueta-Guzmán MP, McFrederick QS, Buchmann SL, Vannette RL, Edlund AF, Mezera CC, Amon N, Danforth BN. Microbes, the 'silent third partners' of bee-angiosperm mutualisms. Trends Ecol Evol 2024; 39:65-77. [PMID: 37940503 DOI: 10.1016/j.tree.2023.09.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 08/30/2023] [Accepted: 09/01/2023] [Indexed: 11/10/2023]
Abstract
While bee-angiosperm mutualisms are widely recognized as foundational partnerships that have shaped the diversity and structure of terrestrial ecosystems, these ancient mutualisms have been underpinned by 'silent third partners': microbes. Here, we propose reframing the canonical bee-angiosperm partnership as a three-way mutualism between bees, microbes, and angiosperms. This new conceptualization casts microbes as active symbionts, processing and protecting pollen-nectar provisions, consolidating nutrients for bee larvae, enhancing floral attractancy, facilitating plant fertilization, and defending bees and plants from pathogens. In exchange, bees and angiosperms provide their microbial associates with food, shelter, and transportation. Such microbial communities represent co-equal partners in tripartite mutualisms with bees and angiosperms, facilitating one of the most important ecological partnerships on land.
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Affiliation(s)
- Shawn A Steffan
- US Department of Agriculture, Agricultural Research Service, 1575 Linden Drive, Madison, WI 53706, USA; Department of Entomology, University of Wisconsin, 1630 Linden Drive, Madison, WI 53706, USA.
| | - Prarthana S Dharampal
- Department of Entomology, University of Wisconsin, 1630 Linden Drive, Madison, WI 53706, USA; Biology Department, McHenry County College, 8900 Northwest Hwy #14, Crystal Lake, IL 60012, USA
| | - Jordan G Kueneman
- Department of Entomology, Cornell University, Comstock Hall, 2126, Ithaca, NY 14853, USA
| | - Alexander Keller
- Cellular and Organismic Networks, Faculty of Biology, Ludwig-Maximilians-Universität München, Martinsried, Germany
| | | | - Quinn S McFrederick
- Department of Entomology, University of California Riverside, Riverside, CA 92521, USA
| | - Stephen L Buchmann
- Department of Entomology, University of Arizona, Tucson, AZ 85721, USA; Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA
| | - Rachel L Vannette
- Department of Entomology and Nematology, University of California, Davis, Davis, CA 95616, USA
| | - Anna F Edlund
- Department of Biology, Bethany College, 31 E Campus Drive, Bethany, WV 26032, USA
| | - Celeste C Mezera
- Department of Entomology, University of Wisconsin, 1630 Linden Drive, Madison, WI 53706, USA
| | - Nolan Amon
- Department of Entomology, University of Wisconsin, 1630 Linden Drive, Madison, WI 53706, USA
| | - Bryan N Danforth
- Department of Entomology, Cornell University, Comstock Hall, 2126, Ithaca, NY 14853, USA
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Khalaf EM, Shrestha A, Reid M, McFadyen BJ, Raizada MN. Conservation and diversity of the pollen microbiome of Pan-American maize using PacBio and MiSeq. Front Microbiol 2023; 14:1276241. [PMID: 38179444 PMCID: PMC10764481 DOI: 10.3389/fmicb.2023.1276241] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Accepted: 11/21/2023] [Indexed: 01/06/2024] Open
Abstract
Pollen is a vector for diversification, fitness-selection, and transmission of plant genetic material. The extent to which the pollen microbiome may contribute to host diversification is largely unknown, because pollen microbiome diversity within a plant species has not been reported, and studies have been limited to conventional short-read 16S rRNA gene sequencing (e.g., V4-MiSeq) which suffers from poor taxonomic resolution. Here we report the pollen microbiomes of 16 primitive and traditional accessions of maize (corn) selected by indigenous peoples across the Americas, along with the modern U.S. inbred B73. The maize pollen microbiome has not previously been reported. The pollen microbiomes were identified using full-length (FL) 16S rRNA gene PacBio SMRT sequencing compared to V4-MiSeq. The Pan-American maize pollen microbiome encompasses 765 taxa spanning 39 genera and 46 species, including known plant growth promoters, insect-obligates, plant pathogens, nitrogen-fixers and biocontrol agents. Eleven genera and 13 species composed the core microbiome. Of 765 taxa, 63% belonged to only four genera: 28% were Pantoea, 15% were Lactococcus, 11% were Pseudomonas, and 10% were Erwinia. Interestingly, of the 215 Pantoea taxa, 180 belonged to a single species, P. ananatis. Surprisingly, the diversity within P. ananatis ranged nearly 10-fold amongst the maize accessions analyzed (those with ≥3 replicates), despite being grown in a common field. The highest diversity within P. ananatis occurred in accessions that originated near the center of diversity of domesticated maize, with reduced diversity associated with the north-south migration of maize. This sub-species diversity was revealed by FL-PacBio but missed by V4-MiSeq. V4-MiSeq also mis-identified some dominant genera captured by FL-PacBio. The study, though limited to a single season and common field, provides initial evidence that pollen microbiomes reflect evolutionary and migratory relationships of their host plants.
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Affiliation(s)
- Eman M. Khalaf
- Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada
- Department of Microbiology and Immunology, Faculty of Pharmacy, Damanhour University, Damanhour, Egypt
| | - Anuja Shrestha
- Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada
| | - Michelle Reid
- Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada
| | | | - Manish N. Raizada
- Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada
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9
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Sasidharan R, Junker RR, Eilers EJ, Müller C. Floral volatiles evoke partially similar responses in both florivores and pollinators and are correlated with non-volatile reward chemicals. ANNALS OF BOTANY 2023; 132:1-14. [PMID: 37220889 PMCID: PMC10550281 DOI: 10.1093/aob/mcad064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Accepted: 05/19/2023] [Indexed: 05/25/2023]
Abstract
BACKGROUND Plants often use floral displays to attract mutualists and prevent antagonist attacks. Chemical displays detectable from a distance include attractive or repellent floral volatile organic compounds (FVOCs). Locally, visitors perceive contact chemicals including nutrients but also deterrent or toxic constituents of pollen and nectar. The FVOC and pollen chemical composition can vary intra- and interspecifically. For certain pollinator and florivore species, responses to these compounds are studied in specific plant systems, yet we lack a synthesis of general patterns comparing these two groups and insights into potential correlations between FVOC and pollen chemodiversity. SCOPE We reviewed how FVOCs and non-volatile floral chemical displays, i.e. pollen nutrients and toxins, vary in composition and affect the detection by and behaviour of insect visitors. Moreover, we used meta-analyses to evaluate the detection of and responses to FVOCs by pollinators vs. florivores within the same plant genera. We also tested whether the chemodiversity of FVOCs, pollen nutrients and toxins is correlated, hence mutually informative. KEY RESULTS According to available data, florivores could detect more FVOCs than pollinators. Frequently tested FVOCs were often reported as pollinator-attractive and florivore-repellent. Among FVOCs tested on both visitor groups, there was a higher number of attractive than repellent compounds. FVOC and pollen toxin richness were negatively correlated, indicating trade-offs, whereas a marginal positive correlation between the amount of pollen protein and toxin richness was observed. CONCLUSIONS Plants face critical trade-offs, because floral chemicals mediate similar information to both mutualists and antagonists, particularly through attractive FVOCs, with fewer repellent FVOCs. Furthermore, florivores might detect more FVOCs, whose richness is correlated with the chemical richness of rewards. Chemodiversity of FVOCs is potentially informative of reward traits. To gain a better understanding of the ecological processes shaping floral chemical displays, more research is needed on floral antagonists of diverse plant species and on the role of floral chemodiversity in visitor responses.
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Affiliation(s)
- Rohit Sasidharan
- Department of Chemical Ecology, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany
| | - Robert R Junker
- Department of Biology, Evolutionary Ecology of Plants, University of Marburg, Karl-von-Frisch-Straße 8, 35043 Marburg, Germany
- Department of Environment and Biodiversity, University of Salzburg, Kapitalgasse 4-6, 5020 Salzburg, Austria
| | - Elisabeth J Eilers
- Department of Chemical Ecology, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany
- CTL GmbH Bielefeld, Krackser Straße 12, 33659 Bielefeld, Germany
| | - Caroline Müller
- Department of Chemical Ecology, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany
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10
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Lazarova S, Lozanova L, Neov B, Shumkova R, Balkanska R, Palova N, Salkova D, Radoslavov G, Hristov P. Composition and diversity of bacterial communities associated with honey bee foragers from two contrasting environments. BULLETIN OF ENTOMOLOGICAL RESEARCH 2023; 113:693-702. [PMID: 37545319 DOI: 10.1017/s0007485323000378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/08/2023]
Abstract
The honey bee is associated with a diverse community of microbes (viruses, bacteria, fungi, and protists), commonly known as the microbiome. Here, we present data on honey bee microbiota from two localities having different surrounding landscapes - mountain (the Rhodope Mountains) and lowland (the Danube plain). The bacterial communities of abdomen of adult bees were studied using amplicon sequencing of the 16S rRNA gene. The composition and dominance structure and their variability within and between localities, alpha and beta diversity, and core and differential taxa were compared at different hierarchical levels (operational taxonomic units to phylum). Seven genera (Lactobacillus, Gilliamella, Bifidobacterium, Commensalibacter, Bartonella, Snodgrassella, and Frischella), known to include core gut-associated phylotypes or species clusters, dominated (92-100%) the bacterial assemblages. Significant variations were found in taxa distribution across both geographical regions and within each apiary. Lactobacillus (Firmicutes) prevailed significantly in the mountain locality followed by Gilliamella and Bartonella (Proteobacteria). Bacteria of four genera, core (Bartonella and Lactobacillus) and non-core (Pseudomonas and Morganella), dominated the bee-associated assemblages of the Danube plain locality. Several ubiquitous bacterial genera (e.g., Klebsiella, Serratia, and Providencia), some species known also as potential and opportunistic bee pathogens, had been found in the lowland locality. Beta diversity analyses confirmed the observed differences in the bacterial communities from both localities. The occurrence of non-core taxa contributes substantially to higher microbial richness and diversity in bees from the Danube plain locality. We assume that the observed differences in the microbiota of honey bees from both apiaries are due to a combination of factors specific for each region. The surrounding landscape features of both localities and related vegetation, anthropogenic impact and land use intensity, the beekeeping management practices, and bee health status might all contribute to observed differences in bee microbiota traits.
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Affiliation(s)
- Stela Lazarova
- Department of Animal Diversity and Resources, Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Lyudmila Lozanova
- Department of Ecosystem Research, Environmental Risk Assessment and Conservation Biology, Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Boyko Neov
- Department of Animal Diversity and Resources, Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Rositsa Shumkova
- Research Centre of Stockbreeding and Agriculture, Agricultural Academy, 4700 Smolyan, Bulgaria
| | - Ralitsa Balkanska
- Department 'Special Branches', Institute of Animal Science, Agricultural Academy, 2230 Kostinbrod, Bulgaria
| | - Nadezhda Palova
- Scientific Center of Agriculture, Agricultural Academy, Sredets 8300, Bulgaria
| | - Delka Salkova
- Department of Experimental Parasitology, Institute of Experimental Morphology, Pathology and Anthropology with Museum, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Georgi Radoslavov
- Department of Animal Diversity and Resources, Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Peter Hristov
- Department of Animal Diversity and Resources, Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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11
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Raguso RA. Hidden worlds within flowers. Curr Biol 2023; 33:R506-R512. [PMID: 37279684 DOI: 10.1016/j.cub.2023.04.054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
There is a growing realization that ecological interactions take place at many scales, from acorns to forests, and that formerly overlooked community members, particularly microbes, can play outsized ecological roles. Beyond their primary function as the reproductive organs of angiosperms, flowers constitute resource-rich, ephemeral habitats teeming with flower-loving symbionts, or 'anthophiles'. The physical, chemical, and structural properties of flowers combine to create a habitat filter, selectively determining which anthophiles can reside there, and how, and when they interact. The microhabitats within flowers can provide shelter from predators or inclement weather, places to eat, sleep, thermoregulate, hunt, mate or reproduce. In turn, floral microhabitats contain the full range of mutualists, antagonists and apparent commensals, whose complex interactions impact how flowers look and smell, how profitable they are to foraging pollinators, and how selection feeds back upon the traits shaping those interactions. Recent studies suggest coevolutionary paths by which floral symbionts might be co-opted as mutualists and provide compelling examples in which ambush predators or florivores are recruited as floral allies. Unbiased studies that include the full roster of floral symbionts are likely to reveal novel links and additional nuance in the rich ecological communities hidden within flowers.
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Affiliation(s)
- Robert A Raguso
- Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA.
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12
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Adomako MO, Yu FH. Potential effects of micro- and nanoplastics on phyllosphere microorganisms and their evolutionary and ecological responses. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 884:163760. [PMID: 37120023 DOI: 10.1016/j.scitotenv.2023.163760] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 04/22/2023] [Accepted: 04/23/2023] [Indexed: 05/05/2023]
Abstract
Plastic pollution is among the most urgent environmental and social challenges of the 21st century, and their influxes in the environment have altered critical growth drivers in all biomes, attracting global concerns. In particular, the consequences of microplastics on plants and their associated soil microorganisms have gained a large audience. On the contrary, how microplastics and nanoplastics (M/NPs) may influence the plant-associated microorganisms in the phyllosphere (i.e., the aboveground portion of plants) is nearly unknown. We, therefore, summarize evidence that may potentially connect M/NPs, plants, and phyllosphere microorganisms based on studies on other analogous contaminants such as heavy metals, pesticides, and nanoparticles. We show seven pathways that may link M/NPs into the phyllosphere environment, and provide a conceptual framework explaining the direct and indirect (soil legacy) effects of M/NPs on phyllosphere microbial communities. We also discuss the adaptive evolutionary and ecological responses, such as acquiring novel resistance genes via horizontal gene transfer and microbial degradation of plastics of the phyllosphere microbial communities, to M/NPs-induced threats. Finally, we highlight the global consequences (e.g., disruption of ecosystem biogeochemical cycling and impaired host-pathogen defense chemistry that can lead to reduced agricultural productivity) of altered plant-microbiome interactions in the phyllosphere in the context of a predicted surge of plastic production and conclude with pending questions for future research priorities. In conclusion, M/NPs are very likely to produce significant effects on phyllosphere microorganisms and mediate their evolutionary and ecological responses.
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Affiliation(s)
- Michael Opoku Adomako
- Institute of Wetland Ecology & Clone Ecology/Zhejiang Provincial Key Laboratory of Plant Evolutionary Ecology and Conservation, Taizhou University, Taizhou 318000, Zhejiang, China
| | - Fei-Hai Yu
- Institute of Wetland Ecology & Clone Ecology/Zhejiang Provincial Key Laboratory of Plant Evolutionary Ecology and Conservation, Taizhou University, Taizhou 318000, Zhejiang, China.
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13
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Fetters AM, Ashman TL. The pollen virome: A review of pollen-associated viruses and consequences for plants and their interactions with pollinators. AMERICAN JOURNAL OF BOTANY 2023:e16144. [PMID: 36924316 DOI: 10.1002/ajb2.16144] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 12/05/2022] [Accepted: 12/06/2022] [Indexed: 06/18/2023]
Abstract
The movement of pollen grains from anthers to stigmas, often by insect pollinator vectors, is essential for plant reproduction. However, pollen is also a unique vehicle for viral spread. Pollen-associated plant viruses reside on the outside or inside of pollen grains, infect susceptible individuals through vertical or horizontal infection pathways, and can decrease plant fitness. These viruses are transferred with pollen between plants by pollinator vectors as they forage for floral resources; thus, pollen-associated viral spread is mediated by floral and pollen grain phenotypes and pollinator traits, much like pollination. Most of what is currently known about pollen-associated viruses was discovered through infection and transmission experiments in controlled settings, usually involving one virus and one plant species of agricultural or horticultural interest. In this review, we first provide an updated, comprehensive list of the recognized pollen-associated viruses. Then, we summarize virus, plant, pollinator vector, and landscape traits that can affect pollen-associated virus transmission, infection, and distribution. Next, we highlight the consequences of plant-pollinator-virus interactions that emerge in complex communities of co-flowering plants and pollinator vectors, such as pollen-associated virus spread between plant species and viral jumps from plant to pollinator hosts. We conclude by emphasizing the need for collaborative research that bridges pollen biology, virology, and pollination biology.
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Affiliation(s)
- Andrea M Fetters
- Department of Biological Sciences, University of Pittsburgh, 4249 Fifth Avenue, Pittsburgh, PA, 15260, USA
- Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, 318 W. 12th Avenue, Columbus, OH, 43210, USA
| | - Tia-Lynn Ashman
- Department of Biological Sciences, University of Pittsburgh, 4249 Fifth Avenue, Pittsburgh, PA, 15260, USA
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14
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Cullen MG, Bliss L, Stanley DA, Carolan JC. Investigating the effects of glyphosate on the bumblebee proteome and microbiota. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 864:161074. [PMID: 36566850 DOI: 10.1016/j.scitotenv.2022.161074] [Citation(s) in RCA: 15] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 12/15/2022] [Accepted: 12/16/2022] [Indexed: 06/17/2023]
Abstract
Glyphosate is one of the most widely used herbicides globally. It acts by inhibiting an enzyme in an aromatic amino acid synthesis pathway specific to plants and microbes, leading to the view that it poses no risk to other organisms. However, there is growing concern that glyphosate is associated with health effects in humans and an ever-increasing body of evidence that suggests potential deleterious effects on other animals including pollinating insects such as bees. Although pesticides have long been considered a factor in the decline of wild bee populations, most research on bees has focussed on demonstrating and understanding the effects of insecticides. To assess whether glyphosate poses a risk to bees, we characterised changes in survival, behaviour, sucrose solution consumption, the digestive tract proteome, and the microbiota in the bumblebee Bombus terrestris after chronic exposure to field relevant doses of technical grade glyphosate or the glyphosate-based formulation, RoundUp Optima+®. Regardless of source, there were changes in response to glyphosate exposure in important cellular and physiological processes in the digestive tract of B. terrestris, with proteins associated with oxidative stress regulation, metabolism, cellular adhesion, the extracellular matrix, and various signalling pathways altered. Interestingly, proteins associated with endocytosis, oxidative phosphorylation, the TCA cycle, and carbohydrate, lipid, and amino acid metabolism were differentially altered depending on whether the exposure source was glyphosate alone or RoundUp Optima+®. In addition, there were alterations to the digestive tract microbiota of bees depending on the glyphosate source No impacts on survival, behaviour, or food consumption were observed. Our research provides insights into the potential mode of action and consequences of glyphosate exposure at the molecular, cellular and organismal level in bumblebees and highlights issues with the current honeybee-centric risk assessment of pesticides and their formulations, where the impact of co-formulants on non-target organisms are generally overlooked.
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Affiliation(s)
- Merissa G Cullen
- Department of Biology, Maynooth University, Maynooth, Co. Kildare, Ireland.
| | - Liam Bliss
- Department of Biology, Maynooth University, Maynooth, Co. Kildare, Ireland
| | - Dara A Stanley
- School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 2, Ireland; Earth Institute, University College Dublin, Belfield, Dublin 2, Ireland
| | - James C Carolan
- Department of Biology, Maynooth University, Maynooth, Co. Kildare, Ireland
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15
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Barberis M, Calabrese D, Galloni M, Nepi M. Secondary Metabolites in Nectar-Mediated Plant-Pollinator Relationships. PLANTS (BASEL, SWITZERLAND) 2023; 12:plants12030550. [PMID: 36771634 PMCID: PMC9920422 DOI: 10.3390/plants12030550] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 01/17/2023] [Accepted: 01/19/2023] [Indexed: 06/01/2023]
Abstract
In recent years, our understanding of the complex chemistry of floral nectar and its ecological implications for plant-pollinator relationships has certainly increased. Nectar is no longer considered merely a reward for pollinators but rather a plant interface for complex interactions with insects and other organisms. A particular class of compounds, i.e., nectar secondary compounds (NSCs), has contributed to this new perspective, framing nectar in a more comprehensive ecological context. The aim of this review is to draft an overview of our current knowledge of NSCs, including emerging aspects such as non-protein amino acids and biogenic amines, whose presence in nectar was highlighted quite recently. After considering the implications of the different classes of NSCs in the pollination scenario, we discuss hypotheses regarding the evolution of such complex nectar profiles and provide cues for future research on plant-pollinator relationships.
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Affiliation(s)
- Marta Barberis
- Department of Biological, Geological and Environmental Sciences, University of Bologna, Via Irnerio 42, 40126 Bologna, Italy
| | - Daniele Calabrese
- Department of Life Sciences, University of Siena, Via P.A. Mattioli 4, 53100 Siena, Italy
| | - Marta Galloni
- Department of Biological, Geological and Environmental Sciences, University of Bologna, Via Irnerio 42, 40126 Bologna, Italy
| | - Massimo Nepi
- Department of Life Sciences, University of Siena, Via P.A. Mattioli 4, 53100 Siena, Italy
- National Biodiversity Future Centre (NBFC), 90123 Palermo, Italy
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16
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Burgess EC, Schaeffer RN. The Floral Microbiome and Its Management in Agroecosystems: A Perspective. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2022; 70:9819-9825. [PMID: 35917340 DOI: 10.1021/acs.jafc.2c02037] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Disease management is critical to ensuring healthy crop yields and is often targeted at flowers because of their susceptibility to pathogens and direct link to reproduction. Many disease management strategies are unsustainable however because of the potential for pathogens to evolve resistance, or nontarget effects on beneficial insects. Manipulating the floral microbiome holds some promise as a sustainable alternative to chemical means of disease control. In this perspective, we discuss the current state of research concerning floral microbiome assembly and management in agroecosystems as well as future directions aimed at improving the sustainability of disease control and insect-mediated ecosystem services.
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Affiliation(s)
- Emily C Burgess
- Department of Biology, Utah State University, Logan, Utah 84322, United States
| | - Robert N Schaeffer
- Department of Biology, Utah State University, Logan, Utah 84322, United States
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17
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Jiménez Elvira N, Ushio M, Sakai S. Are microbes growing on flowers evil? Effects of old flower microbes on fruit set in a wild ginger with one-day flowers, Alpinia japonica (Zingiberaceae). METABARCODING AND METAGENOMICS 2022. [DOI: 10.3897/mbmg.6.84331] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Flowers are colonized and inhabited by diverse microbes. Flowers have various mechanisms to suppress microbial growth, such as flower volatiles, reactive oxygen and secondary compounds. Besides, plants rapidly replace flowers that have a short lifespan, and old flowers senesce. They may contribute to avoiding adverse effects of the microbes. In this study, we investigate if the flower microbial community on old flowers impedes fruit and seed production in a wild ginger with one-day flowers. We focus on microbes on old flowers because they may be composed of microbes that would grow during flowering if the flowers did not have mechanisms to suppress microbial growth. We inoculated newly opened flowers with old flower microbes, and monitored the effects on fruit and seed set. We also assessed prokaryotic communities on the flowers using 16S rRNA amplicon sequencing. We found six bacterial amplicon sequence variants (ASVs) whose proportions were increased on the inoculated flowers. These ASVs were also found on flower buds and flowers that were bagged by net or paper during anthesis, suggesting that they had been present in small numbers prior to flowering. Fruit set was negatively associated with the proportions of these ASVs, while seed set was not. The results suggest that old flowers harbor microbial communities different from those at anthesis, and that the microbes abundant on old flowers negatively affect plant reproduction. Although it has received little attention, antagonistic microbes that rapidly proliferate on the flowers may have affected the evolution of various flower characteristics such as flower volatiles and life span.
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18
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Martin VN, Schaeffer RN, Fukami T. Potential effects of nectar microbes on pollinator health. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210155. [PMID: 35491594 DOI: 10.1098/rstb.2021.0155] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Floral nectar is prone to colonization by nectar-adapted yeasts and bacteria via air-, rain-, and animal-mediated dispersal. Upon colonization, microbes can modify nectar chemical constituents that are plant-provisioned or impart their own through secretion of metabolic by-products or antibiotics into the nectar environment. Such modifications can have consequences for pollinator perception of nectar quality, as microbial metabolism can leave a distinct imprint on olfactory and gustatory cues that inform foraging decisions. Furthermore, direct interactions between pollinators and nectar microbes, as well as consumption of modified nectar, have the potential to affect pollinator health both positively and negatively. Here, we discuss and integrate recent findings from research on plant-microbe-pollinator interactions and their consequences for pollinator health. We then explore future avenues of research that could shed light on the myriad ways in which nectar microbes can affect pollinator health, including the taxonomic diversity of vertebrate and invertebrate pollinators that rely on this reward. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.
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Affiliation(s)
| | | | - Tadashi Fukami
- Department of Biology, Stanford University, Stanford, CA, USA
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19
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Weinhold A. Bowel Movement: Integrating Host Mobility and Microbial Transmission Across Host Taxa. Front Microbiol 2022; 13:826364. [PMID: 35242121 PMCID: PMC8886138 DOI: 10.3389/fmicb.2022.826364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 01/25/2022] [Indexed: 11/22/2022] Open
Abstract
The gut microbiota of animals displays a high degree of plasticity with respect to environmental or dietary adaptations and is shaped by factors like social interactions, diet diversity or the local environment. But the contribution of these drivers varies across host taxa and our ability to explain microbiome variability within wild populations remains limited. Terrestrial animals have divergent mobility ranges and can either crawl, walk or fly, from a couple of centimeters toward thousands of kilometers. Animal movement has been little regarded in host microbiota frameworks, though it can directly influence major drivers of the host microbiota: (1) Aggregation movement can enhance social transmissions, (2) foraging movement can extend range of diet diversity, and (3) dispersal movement determines the local environment of a host. Here, I would like to outline how movement behaviors of different host taxa matter for microbial acquisition across mammals, birds as well as insects. Host movement can have contrasting effects and either reduce or enlarge spatial scale. Increased dispersal movement could dissolve local effects of sampling location, while aggregation could enhance inter-host transmissions and uniformity among social groups. Host movement can also extend the boundaries of microbial dispersal limitations and connect habitat patches across plant-pollinator networks, while the microbiota of wild populations could converge toward a uniform pattern when mobility is interrupted in captivity or laboratory settings. Hence, the implementation of host movement would be a valuable addition to the metacommunity concept, to comprehend microbial dispersal within and across trophic levels.
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Affiliation(s)
- Arne Weinhold
- Faculty of Biology, Cellular and Organismic Networks, Ludwig-Maximilians-Universität München, Munich, Germany
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20
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de Vega C, Albaladejo RG, Álvarez-Pérez S, Herrera CM. Contrasting effects of nectar yeasts on the reproduction of Mediterranean plant species. AMERICAN JOURNAL OF BOTANY 2022; 109:393-405. [PMID: 35315515 DOI: 10.1002/ajb2.1834] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 12/15/2021] [Accepted: 12/17/2021] [Indexed: 06/14/2023]
Abstract
PREMISE Yeasts are often present in floral nectar and can influence plant fitness directly (independently of pollinators) or indirectly by influencing pollinator visitation and behavior. However, few studies have assessed the effect of nectar yeasts on plant reproductive success or compared effects across different plant species, limiting our understanding of the relative impact of direct vs. indirect effects. METHODS We inoculated the nectar of six plant species in the field with the cosmopolitan yeast Metschnikowia reukaufii to analyze the direct and indirect effects on female reproductive success over 2 years. The pollinator assemblage for each species was recorded during both flowering years. RESULTS Direct yeast effects on female fecundity were statistically nonsignificant for all plant species. There were significant indirect, pollinator-mediated effects on fruit production and seed mass for the two species pollinated almost exclusively by bumblebees or hawkmoths, with the direction of the effects differing for the quantity- and quality-related fitness components. There were no consistent effects of the yeast on maternal fecundity for any of the species with diverse pollinator assemblages. CONCLUSIONS Effects of M. reukaufii on plant reproduction ranged from negative to neutral or positive depending on the plant species. The among-species variation in the indirect effects of nectar yeasts on plant pollination could reflect variation in the pollinator community, the specific microbes colonizing the nectar, and the order of microbial infection (priority effects), determining potential species interactions. Elucidating the nature of these multitrophic plant-pollinator-microbe interactions is important to understand complex processes underlying plant pollination.
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Affiliation(s)
- Clara de Vega
- Departamento de Biología Vegetal y Ecología, Facultad de Farmacia, Universidad de Sevilla, Calle Profesor García González n 2. 41012 Sevilla, Spain
| | - Rafael G Albaladejo
- Departamento de Biología Vegetal y Ecología, Facultad de Farmacia, Universidad de Sevilla, Calle Profesor García González n 2. 41012 Sevilla, Spain
| | - Sergio Álvarez-Pérez
- Department of Animal Health, Faculty of Veterinary Medicine, Complutense University of Madrid, Avenida Puerta de Hierro s/n, 28040, Madrid, Spain
| | - Carlos M Herrera
- Estación Biológica de Doñana, Consejo Superior de Investigaciones Científicas, Avenida Américo Vespucio 26, E-41092, Sevilla, Spain
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21
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Wei N, Whyle RL, Ashman TL, Jamieson MA. Genotypic variation in floral volatiles influences floral microbiome more strongly than interactions with herbivores and mycorrhizae in strawberriesd. HORTICULTURE RESEARCH 2022; 9:uhab005. [PMID: 35141759 PMCID: PMC8795819 DOI: 10.1093/hr/uhab005] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 01/18/2022] [Accepted: 10/15/2021] [Indexed: 06/14/2023]
Abstract
The floral microbiome is of significant relevance to plant reproduction and crop productivity. While plant genotype is key to floral microbiome assembly, whether and how genotypic variation in floral traits and plant-level mutualistic and antagonistic interactions at the rhizosphere and phyllosphere influence the microbiome in the anthosphere remain little known. Using a factorial field experiment that manipulated biotic interactions belowground (mycorrhizae treatments) and aboveground (herbivory treatments) in three strawberry genotypes, we assessed how genotypic variation in flower abundance and size and plant-level biotic interactions influence the bidirectional relationships between floral volatile organic compounds (VOCs) and the floral microbiome using structural equation modeling. We found that plant genotype played a stronger role, overall, in shaping the floral microbiome than biotic interactions with mycorrhizae and herbivores. Genotypic variation in flower abundance and size influenced the emission of floral VOCs, especially terpenes (e.g. α- and β-pinene, ocimene isomers) and benzenoids (e.g. p-anisaldehyde, benzaldehyde), which in turn affected floral bacterial and fungal communities. While the effects of biotic interactions on floral traits including VOCs were weak, mycorrhizae treatments (mycorrhizae and herbivory + mycorrhizae) affected the fungal community composition in flowers. These findings improve our understanding of the mechanisms by which plant genotype influences floral microbiome assembly and provide the first evidence that biotic interactions in the rhizosphere and phyllosphere can influence the floral microbiome, and offer important insights into agricultural microbiomes.
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Affiliation(s)
- Na Wei
- The Holden Arboretum, Kirtland, OH 44094, USA
- Department of Biological Sciences, University of Pittsburg, Pittsburg, PA 15260, USA
| | - Robert L Whyle
- Department of Biological Sciences, Oakland University, Rochester, MI 48309, USA
| | - Tia-Lynn Ashman
- Department of Biological Sciences, University of Pittsburg, Pittsburg, PA 15260, USA
| | - Mary A Jamieson
- Department of Biological Sciences, Oakland University, Rochester, MI 48309, USA
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22
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Crowley B, Russell A. Plant biology: Nectar bacteria grow by germinating and bursting pollen. Curr Biol 2021; 31:R1120-R1122. [PMID: 34637711 DOI: 10.1016/j.cub.2021.08.024] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Microbial residents of floral nectar must survive in a carbohydrate-rich yet seemingly nitrogen-poor environment. A new study shows that Acinetobacter spp., common nectar-inhabiting bacteria, differentially induce the pollen commonly found in nectar to germinate and burst, releasing nutrients for microbial growth.
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Affiliation(s)
- Bailey Crowley
- Department of Biology, Utah State University, Logan, UT 84322, USA
| | - Avery Russell
- Department of Biology, Missouri State University, Springfield, MO 65897, USA.
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23
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Evolutionary and Ecological Considerations on Nectar-Mediated Tripartite Interactions in Angiosperms and Their Relevance in the Mediterranean Basin. PLANTS 2021; 10:plants10030507. [PMID: 33803275 PMCID: PMC7999006 DOI: 10.3390/plants10030507] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 02/22/2021] [Accepted: 03/03/2021] [Indexed: 11/16/2022]
Abstract
The Mediterranean basin hosts a high diversity of plants and bees, and it is considered one of the world's biodiversity hotspots. Insect pollination, i.e., pollen transfer from male reproductive structures to conspecific female ones, was classically thought to be a mutualistic relationship that links these two groups of organisms, giving rise to an admirable and complex network of interactions. Although nectar is often involved in mediating these interactions, relatively little is known about modifications in its chemical traits during the evolution of plants. Here, we examine how the current sucrose-dominated floral nectar of most Mediterranean plants could have arisen in the course of evolution of angiosperms. The transition from hexose-rich to sucrose-rich nectar secretion was probably triggered by increasing temperature and aridity during the Cretaceous period, when most angiosperms were radiating. This transition may have opened new ecological niches for new groups of insects that were co-diversifying with angiosperms and for specific nectar-dwelling yeasts that originated later (i.e., Metschnikowiaceae). Our hypothesis embeds recent discoveries in nectar biology, such as the involvement of nectar microbiota and nectar secondary metabolites in shaping interactions with pollinators, and it suggests a complex, multifaceted ecological and evolutionary scenario that we are just beginning to discover.
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