The objective of this proposal is to define the genetic system that controls expression of the hypersensitive response (HR) elicited by Pseudomonas solanacearum in plant hosts and non-hosts. Dr. Sequeira has obtained a series of genetically defined, transposon-generated mutants from both HR+ and HR- parental strains. He has also determined that the hypersensitive response is induced by plant signal molecules and, from one parental strain, he has purified a 60kD protein that appears to be responsible for the tissue browning and collapse associated with the hypersensitive response. He proposes to utilize the HR- mutants to define the role of this 60kD protein in the response caused by P. solanacearum in tobacco, potato, and cucumber. He also proposes structural and functional analyses of the genes that code for the hypersensitive response when these genes function in different genetic and phenotypic backgrounds. The aim is to determine the role that HR plays in host specificity. A final objective is to determine the nature of the signal molecules from the host that may be involved in activation of HR genes in P. solanacearum. This study will enhance our understanding of plant-bacterial interactions in general and specifically, process of tissue browning and collapse associated with the hypersensitive reaction in plant hosts in response to infection by bacteria.
