Dr. Jacobs proposes to isolate, characterize and begin a developmental analysis of plant genes activated by Rhizobium. This includes obtaining cDNA clones for any genes which exhibit transcriptional induction at the earliest stages of Rhizobium infection. Using heterologous probes from well-characterized plant systems, he will also obtain cDNA clones for defined genes which are expected to play a role in root dedifferentiation and nodule meristem induction. Genes expected to be activated by Rhizobium infection include those encoding cell division functions and cytoskeletal elements such as actin, tubulin and extensin. Recovered clones will be analyzed in several ways. First, clones will be confirmed by Northern analysis to assure the presumed developmental relevance of their cognate genes. Next, the cDNA clones will be restriction mapped and subcloned into plasmid vectors. These subclones will be used for analysis of the activation of their cognate genes, as influenced by mutant bacterial and host plant genotypes, by cell-free extracts of activated rhizobia and by abiotic factors such as calcium and nitrogen availability during inoculation. Dr. Jacobs has begun a molecular analysis of the plant genes during the Rhizobium/legume symbiosis. This symbiotic interaction is important in a practical way for the assimilation of nitrogen by the plant but also can be a useful model for differential plant gene expression during organogenesis.
