Mutualism Stability in the Rhizobia-Legume Symbiosis

Abstract
Rhizobia and legumes form a mutualistic relationship that supports biological nitrogen fixation, a process essential for enriching soil in agricultural ecosystems. In this partnership, legumes receive nitrogen from rhizobia, which convert atmospheric nitrogen into a usable form, while the bacteria obtain carbon from the plant's photosynthesis. Both partners use these resources to enhance their fitness—promoting growth and reproduction. The stability of this mutualism depends on their interests being aligned; if their interests are in conflict, the relationship can break down. My research focuses on rhizobial genes that may simultaneously influence the fitness of both the plant and the bacteria. These genes were identified using Genome-Wide Association Studies (GWAS), though their role in mutualism has not been studied before. To investigate and validate their function, I have created rhizobial mutants by disrupting nine specific genes. Using a randomized block design in a greenhouse experiment, I inoculated these mutants either individually or in combination with wild-type rhizobia in two Medicago truncatula ecotypes, A17 and DZA. I have collected data on traits related to both plant and rhizobial fitness. Additionally, I am evaluating the effect of these mutants on rhizobial competitive fitness in their free-living stage

About the Speaker
My name is Maria Alejandra Gil Polo, and I am entering my fifth year as a PhD student in the Plant Biology program. I was born in Peru, where I earned my bachelor's degree in Biology with a mention in Biotechnology from Universidad Nacional Agraria La Molina. As an undergraduate research assistant, I spent four years working in the Microbial Ecology and Biotechnology Lab, studying plant growth-promoting rhizobacteria and their interactions, ranging from antagonistic to mutualistic. My research later shifted toward genetic engineering for functional genomics of rhizobial secretion systems following a research visit to the Center for Biotechnology and Genomics of Plants in Spain and an internship at Cornell University, where I trained in synthetic biology tools. Currently, in the Burghardt Lab, I study the ecology and evolution of rhizobia both within and beyond their mutualistic interactions with plants.

Contact

Liana Burghardt
liana.burghardt@psu.edu