Physiological and molecular analysis of plant-microbe interactions in the rhizosphere

Besides offering mechanical support and absorbing water and nutrients from the soil, plant root help to sense and respond to soil environment. Plant root often respond to biotic and/or abiotic cues by secreting a mixture of chemical compounds commonly referred to as root exudates. One group of organisms that interact with plant roots in the rhizosphere (the soil zone extending to a few millimeters immediately surrounding the root) is bacteria, a group consisting of both pathogenic and beneficial forms. Chemical components present in the root exudates affect the growth and physiology of bacteria, implying a dynamic interaction between rhizosphere bacteria and the plant root. The chemical components and the biological functions of the root exudates on pathogenic and beneficial root-bacteria interaction, and the genetic basis of the interactions are largely unknown. The proposed research program will use the existing vast genetic resource of Arabidopsis thaliana to identify components in the root exudates that promote colonization by beneficial Pseudomonas putida and those that repel pathogenic Pseduomonas syringae pv tomato DC3000. Furthermore, this program will unravel the genetic basis of root-microbe interactions. In the short term, chemical analysis of root exudates and associated gene expression will lead to the development of metabolic and molecular markers that could be used to identify genotypes that selectively encourage the population of beneficial bacteria in the rhizosphere. Taken together, this research program will add considerable new knowledge to our current understanding of rhizosphere plant-microbe interactions.