9418975 Lawton This award deals with the PR5K gene from Arabidopsis thaliana which encodes a novel receptor with structural features related to plant defense proteins. The kinase domain of PR5K is presumed to be involved in cytoplasmic signal transduction. The extracellular domain is closely related to a group of antimicrobial proteins that includes the pathogenesis protein PR-5, osmotin, thaumatin and a bifunctional inhibitor of maize. By analogy with other receptor kinases, this domain is the predicted binding site for a polypeptide ligand. The structural relationship between the extracellular domain of PR5K and known pathogenesis-related proteins suggests a possible functional relationship in the expression of the defense response. Thus, cellular targets of antimicrobial proteins such as PR5 might also serve as ligands for activation of the PR5K receptor. A close structural relationship is also seen for the secreted and kinase-linked forms of the S-locus glycoproteins of Brassica and these molecules have been proposed to form a functional unit that specifies self- incompatibility during pistil-pollen interactions. This proposal is concerned with characterizing the PR5K receptor and dissecting its possible role in the perception of plant defense signals.
