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Williamson J, Matthews AC, Raymond B. Competition and co-association, but not phosphorous availability, shape the benefits of phosphate-solubilizing root bacteria for maize ( Zea mays). Access Microbiol 2023; 5:000543.v3. [PMID: 38188242 PMCID: PMC10765048 DOI: 10.1099/acmi.0.000543.v3] [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] [Received: 12/09/2022] [Accepted: 11/16/2023] [Indexed: 01/09/2024] Open
Abstract
Predicting the conditions under which rhizobacteria benefit plant growth remains challenging. Here we tested the hypothesis that benefits from inoculation with phosphate-solubilizing rhizobacteria will depend upon two environmental conditions: phosphate availability and competition between bacteria. We used maize-associated rhizobacteria with varying phosphate solubilization ability in experiments in soil, sterilized soil and gnotobiotic microcosms under conditions of varying orthophosphate availability, while we manipulated the intensity of competition by varying the number of isolates in plant inocula. Growth promotion by microbes did not depend on phosphate availability but was affected by interactions between inoculants: the beneficial effects of one Serratia isolate were only detectable when plants were inoculated with a single strain and the beneficial effects of a competition-sensitive Rhizobium was only detectable in sterilized soil or in microcosms inoculated with single strains. Moreover, microcosm experiments suggested that facilitation of a parasitic isolate, not competitive interactions between bacteria, prevented plants from gaining benefits from a potential mutualist. Competition and facilitation affected colonization of plants in microcosms but growth promotion by Serratia was more affected by inoculation treatment than culturable densities on roots. Experimental manipulation of seed inocula can reveal whether plant growth stimulation is robust with respect to competition, as well as the ecological strategies of different rhizobacteria. From an applied perspective, phosphate solubilization may not provide the mechanism for bacterial growth promotion but may indicate mutualistic potential due to phylogenetic associations. Importantly, benefits to plants are vulnerable to interactions between rhizobacteria and may not persist in mixed inoculations.
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Affiliation(s)
- Joseph Williamson
- Department of Life Sciences, Silwood Park campus, Imperial College London, Ascot, SL5 7PY, UK
- Centre for Biodiversity and Environment Research, Department of Genetics, University College London, Gower St, London, WC1E 6BT, UK
| | - Andrew Charles Matthews
- Department of Life Sciences, Silwood Park campus, Imperial College London, Ascot, SL5 7PY, UK
- College of Life and Environmental Sciences, Penryn campus, University of Exeter, Penryn, TR10 9FE, UK
| | - Ben Raymond
- Department of Life Sciences, Silwood Park campus, Imperial College London, Ascot, SL5 7PY, UK
- College of Life and Environmental Sciences, Penryn campus, University of Exeter, Penryn, TR10 9FE, UK
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Sullivan TJ, Roberts H, Bultman TL. Genetic Covariation Between the Vertically Transmitted Endophyte Epichloë canadensis and Its Host Canada Wildrye. MICROBIAL ECOLOGY 2023; 86:1686-1695. [PMID: 36725749 DOI: 10.1007/s00248-022-02166-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Accepted: 12/26/2022] [Indexed: 06/18/2023]
Abstract
Symbiotic mutualisms are thought to be stabilized by correlations between the interacting genotypes which may be strengthened via vertical transmission and/or reduced genetic variability within each species. Vertical transmission, however, may weaken interactions over time as the endosymbionts would acquire mutations that could not be purged. Additionally, temporal variation in a conditional mutualism could create genetic variation and increased variation in the interaction outcome. In this study, we assessed genetic variation in both members of a symbiosis, the endosymbiotic fungal endophyte Epichloë canadensis and its grass host Canada wildrye (Elymus canadensis). Both species exhibited comparable levels of diversity, mostly within populations rather than between. There were significant differences between populations, although not in the same pattern for the two species, and the differences were not correlated with geographic distance for either species. Interindividual genetic distance matrices for the two species were significantly correlated, although all combinations of discriminant analysis of principle components (DAPC) defined multilocus genotype groups were found suggesting that strict genotype matching is not necessary. Variation in interaction outcome is common in grass/endophyte interactions, and our results suggest that the accumulation of mutations overtime combined with temporal variation in selection pressures increasing genetic variation in the symbiosis may be the cause.
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Affiliation(s)
- T J Sullivan
- School of Sciences, Indiana University Kokomo, 2300 S. Washington St, Kokomo, IN, 46902, USA.
| | - Holly Roberts
- School of Sciences, Indiana University Kokomo, 2300 S. Washington St, Kokomo, IN, 46902, USA
| | - Thomas L Bultman
- Department of Biology, Hope College, 35 E. 12th St., Holland, MI, 49423, USA
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Decunta FA, Pérez LI, Malinowski DP, Molina-Montenegro MA, Gundel PE. A Systematic Review on the Effects of Epichloë Fungal Endophytes on Drought Tolerance in Cool-Season Grasses. FRONTIERS IN PLANT SCIENCE 2021; 12:644731. [PMID: 33841472 PMCID: PMC8025668 DOI: 10.3389/fpls.2021.644731] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 02/18/2021] [Indexed: 05/17/2023]
Abstract
Symptomless fungal endophytes in the genus Epichloë are repeatedly mentioned to increase tolerance of cool-season grasses to a wide range of environmental stress factors, mainly drought. However, the generality of this idea is challenged because (i) most studies have been conducted on two economically important forage grasses {tall fescue [Festuca arundinacea (Schreb.) Dumort] and perennial ryegrass (Lolium perenne L.)}, (ii) endophyte-mediated mechanisms and effects on plant responses to drought have shown to be highly variable across species, and that (iii) symbiosis incidence in plant populations occurring in extremely arid environments is usually low. We question this idea by reviewing the existing information about Epichloë fungal endophyte effects on drought tolerance in cool-season grasses. We combined standard review, vote counting, and calculation of effect sizes to synthesize the literature, identify information gaps, and guide future research. The total number of studies was higher for domesticated than for wild species, a ratio that was balanced when papers with data quality for effect size calculus were considered. After the drought, endophyte-infected plants accumulated more aboveground and belowground biomass than non-infected counterparts, while no effect on tillering was observed. However, these effects remained significant for wild (even on tillering) but not for domesticated species. Interestingly, despite the continuous effort in determining physiological mechanisms behind the endophyte effects, no studies evaluated plant fecundity as a measure of ecological fitness nor vital rates (such as survival) as to escalate individual-level variables to population. Together with the high variability in results, our work shows that generalizing a positive effect of fungal endophytes in plant tolerance to drought may be misleading. Future studies combining field surveys with manipulative experiments would allow us to unravel the role of fungal endophytes in plant adaptation by considering the evolutionary history of species and populations to the different ecological contexts.
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Affiliation(s)
- Facundo A. Decunta
- Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA), Facultad de Agronomía, Buenos Aires, Argentina
- *Correspondence: Facundo A. Decunta
| | - Luis I. Pérez
- Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA), Facultad de Agronomía, Buenos Aires, Argentina
| | | | - Marco A. Molina-Montenegro
- Instituto de Ciencias Biológicas, Universidad de Talca, Talca, Chile
- Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Universidad Católica del Norte, Coquimbo, Chile
- Centro de Investigaciones y Estudios Avanzados del Maule (CIEAM), Universidad Católica del Maule, Talca, Chile
| | - Pedro E. Gundel
- Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA), Facultad de Agronomía, Buenos Aires, Argentina
- Instituto de Ciencias Biológicas, Universidad de Talca, Talca, Chile
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Gundel PE, Sun P, Charlton ND, Young CA, Miller TEX, Rudgers JA. Simulated folivory increases vertical transmission of fungal endophytes that deter herbivores and alter tolerance to herbivory in Poa autumnalis. ANNALS OF BOTANY 2020; 125:981-991. [PMID: 32010946 PMCID: PMC7218812 DOI: 10.1093/aob/mcaa021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 01/31/2020] [Indexed: 05/02/2023]
Abstract
BACKGROUND AND AIMS The processes that maintain variation in the prevalence of symbioses within host populations are not well understood. While the fitness benefits of symbiosis have clearly been shown to drive changes in symbiont prevalence, the rate of transmission has been less well studied. Many grasses host symbiotic fungi (Epichloë spp.), which can be transmitted vertically to seeds or horizontally via spores. These symbionts may protect plants against herbivores by producing alkaloids or by increasing tolerance to damage. Therefore, herbivory may be a key ecological factor that alters symbiont prevalence within host populations by affecting either symbiont benefits to host fitness or the symbiont transmission rate. Here, we addressed the following questions: Does symbiont presence modulate plant tolerance to herbivory? Does folivory increase symbiont vertical transmission to seeds or hyphal density in seedlings? Do plants with symbiont horizontal transmission have lower rates of vertical transmission than plants lacking horizontal transmission? METHODS We studied the grass Poa autumnalis and its symbiotic fungi in the genus Epichloë. We measured plant fitness (survival, growth, reproduction) and symbiont transmission to seeds following simulated folivory in a 3-year common garden experiment and surveyed natural populations that varied in mode of symbiont transmission. KEY RESULTS Poa autumnalis hosted two Epichloë taxa, an undescribed vertically transmitted Epichloë sp. PauTG-1 and E. typhina subsp. poae with both vertical and horizontal transmission. Simulated folivory reduced plant survival, but endophyte presence increased tolerance to damage and boosted fitness. Folivory increased vertical transmission and hyphal density within seedlings, suggesting induced protection for progeny of damaged plants. Across natural populations, the prevalence of vertical transmission did not correlate with symbiont prevalence or differ with mode of transmission. CONCLUSIONS Herbivory not only mediated the reproductive fitness benefits of symbiosis, but also promoted symbiosis prevalence by increasing vertical transmission of the fungus to the next generation. Our results reveal a new mechanism by which herbivores could influence the prevalence of microbial symbionts in host populations.
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Affiliation(s)
- Pedro E Gundel
- IFEVA-CONICET, Department of Ecology, College of Agronomy, University of Buenos Aires, Buenos Aires, Argentina
- Department of Biology, University of New Mexico, Albuquerque, NM, USA
- For correspondence. E-mail
| | - Prudence Sun
- Department of Biosciences, Rice University, Houston, TX, USA
| | | | | | - Tom E X Miller
- Department of Biosciences, Rice University, Houston, TX, USA
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Sneck ME, Rudgers JA, Young CA, Miller TEX. Does host outcrossing disrupt compatibility with heritable symbionts? OIKOS 2019. [DOI: 10.1111/oik.06182] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Michelle E. Sneck
- Dept of BioSciences, Program in Ecology and Evolutionary Biology, Rice Univ Houston, TX 77005 USA
| | | | | | - Tom E. X. Miller
- Dept of BioSciences, Program in Ecology and Evolutionary Biology, Rice Univ Houston, TX 77005 USA
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Shymanovich T, Faeth SH. Environmental factors affect the distribution of two Epichloë fungal endophyte species inhabiting a common host grove bluegrass ( Poa alsodes). Ecol Evol 2019; 9:6624-6642. [PMID: 31236248 PMCID: PMC6580270 DOI: 10.1002/ece3.5241] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Revised: 04/17/2019] [Accepted: 04/18/2019] [Indexed: 01/24/2023] Open
Abstract
AIM The endophyte Epichloë alsodes, with known insecticidal properties, is found in a majority of Poa alsodes populations across a latitudinal gradient from North Carolina to New York. A second endophyte, E. schardlii var. pennsylvanica, with known insect-deterring effects, is limited to a few populations in Pennsylvania. We explored whether such disparate differences in distributions could be explained by selection from biotic and abiotic environmental factors. LOCATION Along the Appalachian Mountains from North Carolina to New York, USA. TAXON Fungi. METHODS Studied correlations of infection frequencies with abiotic and biotic environmental factors. Checked endophyte vertical transmission rates and effects on overwintering survival. With artificial inoculations for two host populations with two isolates per endophyte species, tested endophyte-host compatibility. Studied effects of isolates on host performances in greenhouse experiment with four water-nutrients treatments. RESULTS Correlation analysis revealed positive associations of E. alsodes frequency with July Max temperatures, July precipitation, and soil nitrogen and phosphorous and negative associations with insect damage and soil magnesium and potassium. Plants infected with E. alsodes had increased overwintering survival compared to plants infected with E. schardlii or uninfected (E-) plants. Artificial inoculations indicated that E. alsodes had better compatibility with a variety of host genotypes than did E. schardlii. The experiment with reciprocally inoculated plants grown under different treatments revealed a complexity of interactions among hosts, endophyte species, isolate within species, host plant origin, and environmental factors. Neither of the endophyte species increased plant biomass, but some of the isolates within each species had other effects on plant growth such as increased root:shoot ratio, number of tillers, and changes in plant height that might affect host fitness. MAIN CONCLUSION In the absence of clear and consistent effects of the endophytes on host growth, the differences in endophyte-mediated protection against herbivores may be the key factor determining distribution differences of the two endophyte species.
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Affiliation(s)
- Tatsiana Shymanovich
- Biology DepartmentUniversity of North Carolina at GreensboroGreensboroNorth Carolina
| | - Stanley H. Faeth
- Biology DepartmentUniversity of North Carolina at GreensboroGreensboroNorth Carolina
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Cavazos BR, Bohner TF, Donald ML, Sneck ME, Shadow A, Omacini M, Rudgers JA, Miller TEX. Testing the roles of vertical transmission and drought stress in the prevalence of heritable fungal endophytes in annual grass populations. THE NEW PHYTOLOGIST 2018; 219:1075-1084. [PMID: 29786864 DOI: 10.1111/nph.15215] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 04/08/2018] [Indexed: 05/22/2023]
Abstract
Beneficial inherited symbionts are expected to reach high prevalence in host populations, yet many are observed at intermediate prevalence. Theory predicts that a balance of fitness benefits and efficiency of vertical transmission may interact to stabilize intermediate prevalence. We established populations of grass hosts (Lolium multiflorum) that varied in prevalence of a heritable fungal endophyte (Epichloё occultans), allowing us to infer long-term equilibria by tracking change in prevalence over one generation. We manipulated an environmental stressor (elevated precipitation), which we hypothesized would reduce the fitness benefits of symbiosis, and altered the efficiency of vertical transmission by replacing endophyte-positive seeds with endophyte-free seeds. Endophytes and elevated precipitation both increased host fitness, but symbiont effects were not stronger in the drier treatment, suggesting that benefits of symbiosis were unrelated to drought tolerance. Reduced transmission suppressed the inferred equilibrium prevalence from 42.6% to 11.7%. However, elevated precipitation did not modify prevalence, consistent with the result that it did not modify fitness benefits. Our results demonstrate that failed transmission can influence the prevalence of heritable microbes and that intermediate prevalence can be a stable equilibrium due to forces that allow symbionts to increase (fitness benefits) but prevent them from reaching fixation (failed transmission).
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Affiliation(s)
- Brittany R Cavazos
- Department of BioSciences, Program in Ecology and Evolutionary Biology, Rice University, Houston, TX, 77005, USA
| | - Teresa F Bohner
- Department of BioSciences, Program in Ecology and Evolutionary Biology, Rice University, Houston, TX, 77005, USA
| | - Marion L Donald
- Department of BioSciences, Program in Ecology and Evolutionary Biology, Rice University, Houston, TX, 77005, USA
| | - Michelle E Sneck
- Department of BioSciences, Program in Ecology and Evolutionary Biology, Rice University, Houston, TX, 77005, USA
| | - Alan Shadow
- USDA NRCS East Texas Plant Materials Center, 6598 FM 2782, Nacogdoches, TX, 75964, USA
| | - Marina Omacini
- IFEVA - Facultad de Agronomıa, Universidad de Buenos Aires, CONICET, Av. San Martın 4453, Buenos Aires, C1417DSE, Argentina
| | - Jennifer A Rudgers
- Department of Biology, University of New Mexico, Albuquerque, NM, 87131, USA
| | - Tom E X Miller
- Department of BioSciences, Program in Ecology and Evolutionary Biology, Rice University, Houston, TX, 77005, USA
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