Stabilizing mechanisms in a legume-rhizobium mutualism
1Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108, USA. katy.heath@utoronto.ca
Evolution; International Journal of Organic Evolution
|December 18, 2008
Summary
Plants can choose beneficial rhizobia partners, promoting mutualism stability. This study shows Medicago truncatula favors more helpful rhizobium strains, influencing their populations over generations.
Area of Science:
- Ecology
- Evolutionary Biology
- Microbiology
Background:
- Mutualisms, like legume-rhizobium symbiosis, can be threatened by less beneficial 'cheater' genotypes.
- Partner choice and sanctioning are hypothesized mechanisms to maintain mutualism integrity.
- The role of these mechanisms in natural settings remains under investigation.
Purpose of the Study:
- To investigate partner choice and sanctioning in Medicago truncatula-rhizobium mutualisms.
- To determine if plants preferentially reward beneficial rhizobia partners.
- To assess the impact of partner choice on rhizobium population dynamics over multiple generations.
Main Methods:
- Grew 12 Medicago truncatula maternal families with a mix of three native rhizobium strains for three generations.
- Quantified symbiotic benefits by measuring nodule number and size conferred to each rhizobium strain.
- Analyzed changes in the relative frequency of rhizobium strains across plant generations.
Main Results:
- The majority of Medicago truncatula genotypes formed more nodules with more beneficial rhizobium strains, indicating adaptive partner choice.
- Three generations of symbiosis led to an increased frequency of the most beneficial rhizobium strains, showing partner choice impacts rhizobium fitness.
- No evidence was found for postnodulation sanctioning affecting nodule size.
Conclusions:
- Medicago truncatula plants exhibit adaptive partner choice, favoring beneficial rhizobia during early symbiosis stages.
- Partner choice mechanisms play a significant role in stabilizing legume-rhizobium mutualisms.
- Coevolutionary signaling between plants and rhizobia is likely influenced by these interactions.
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