NSF Award
2217901
Mutualisms are of fundamental importance and found at every organismal level, where they facilitate the fitness and survival of the interacting partners. For example, nitrogen is an essential nutrient required for plant growth, yet the most abundant form is inaccessible to plants, making it a limiting resource. Legumes have overcome this limitation by forming beneficial partnerships with symbiotic bacteria, known as rhizobia, where they receive usable nitrogen in exchange for carbon metabolites. The problem is that prior to establishing the relationship, the plant has no information about the quality of its partner. Choosing the right mutualistic bacterial partner, while excluding parasitic bacteria, is essential because the process to form the mutualistic relationship requires the plant to expend energy that could otherwise be used for growth. Many legume species already show some degree of specificity using signaling to limit partnership with compatible rhizobia species. Once the partnership is initiated, there is additional molecular signaling that triggers the plant immune system. Either type of signaling may leave an imprint or memory on the host plant that is specific to individual rhizobia strains. This study examines the hypothesis that this memory may be heritable and help future generations of the host plant choose beneficial strains due to familiarity, giving a better understanding of non-genetic heritability and providing insight into the maintenance of mutualistic relationships. This project also provides undergraduate students with funded research experience, which has been shown to improve diversity and increase retention in STEM.<br/><br/>The origination and maintenance of mutualisms presents an evolutionary conundrum as both partners are expected to act in their own self-interest. As with all mutualisms, there is a risk of the host being exploited by their partner leading to the breakdown of the relationship. The ability to choose a faithful and beneficial partner can stabilize the partnership. However, the mechanism that allows for partner choice has not yet been uncovered in the legume-rhizobia mutualism, despite evidence that host plants are able to preferentially nodulate with more beneficial partners. This project examines the prediction that the selected partner will likely be determined through a combination of genetic (host plant and rhizobia genes), epigenetic and environmental elements. Using the bearded clover, Trifolium barbigerum, the research team will determine whether transgenerational effects from previous generations can influence the host plant’s choice of symbiotic partner. This project will quantify nodule occupancy to determine whether previous exposure to a strain and its efficacy inform host plant selection using a combination of fluorescent labeling, qPCR and metabarcoding to distinguish rhizobia at the strain level.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
