Plant Symbiote Methylorubrum extorquens Aids in Plant Defense Priming via Exogenous Riboflavin
Plants prepare themselves for stress by altering chromatin structures via a phenomenon called defense priming. Priming can be achieved through factors called priming agents, which are abiotic or biotic non-stressors, such as minerals, vitamins, or symbiotic microbes. One known plant symbiote, Methylorubrum extorquens, dominates colonization of plant leaves to metabolize methanol while offering some protection from harmful bacteria. Riboflavin has been documented as a powerful priming agent against biotic stress. We hypothesized that there is a link between the priming effects of riboflavin and M. extorquens on plant defense. This experiment sought to visualize the relationships between plant model Arabidopsis thaliana, sterile or colonized by M. extorquens, treated with riboflavin as a priming agent. To do so, A. thaliana biotic stress response genes were selected. Plants were either treated with stressor (peptide flg22) or primer (riboflavin). Treated plants had their RNA extracted and analyzed by qRT-PCR in order to determine the relative expression levels of each gene of interest. Results indicated a relationship between the genes and both riboflavin and M. extorquens, with inoculated plants inducing a stronger effect on the relative expression. This suggests that M. extorquens may have a role in the pathway of priming through riboflavin. Interestingly, inoculated plants also had stronger relative expression levels for genes that are negative regulators of the stress response. This may be because these genes block senescence, and allow the bacteria to grow more successfully. Future studies should test which compounds M. extorquens release that triggers the plant defense response, whether or not riboflavin-synthesizing mutants of M. extorquens can yield the same results, or how these results would vary in the presence of plant pathogens.