MCB-9417732 Walker Differentiation in plants is profoundly affected by environmental factors. The long term goal of our research is to understand how extracellular signals interact with the plant cellular machinery to influence growth and development. Recent evidence strongly suggests that plant cells have plasma membrane receptors with intrinsic protein kinase activity. The plant receptor-like protein kinases (RLK) are structurally related to the animal polypeptide growth factor receptors; however, the plant RLKs all appear to be serine/threonine protein kinases. Diversity among plant RLKs, reflected in their structural and functional properties, has opened up a broad new area of investigation into cellular signaling in plants with far-reaching implications for the mechnaisms by which plant cells perceive and respond to extracellular stimuli. Our specific aims are to characterize the biochemical properties, both in vitro and in vivo, of one receptor-like protein kinase (RLK5) from Arabidopsis thaliana. We have shown that a recombinant fusion protein of this transmembrane protein kinase will autophosphorylate several sites and that autophosphorylation is critical for interaction with cellular targets. One of these targets, KAPP (kinase associated protein phosphatase) contains three domains: an amino-terminal membrane insertion signal, a kinase interaction domain and phosphoprotein phosphatase domain, Interaction of KAPP with RLK5 requires RLK5 phosphorylation. This mechanism of binding is reminiscent of the interaction of src homology 2 containing proteins with activated growth factor receptors in animals. The research proposed here will define the autophosphorylation sites in RLK5 and investigate the functional significance of KAPP binding to RLK5. Additional components for RLK5 mediated intracellular signaling will also be identified. It is anticipated that results from these studies will yield fundamental and new insights into the molecular mech anisms of how plants perceive their environment and how growth and developmental processes are regulated by environmental signals. %%% Differentiation in plants is profoundly affected by environmental factors. The long term goal of our research is to understand how extracellular signals interact with the plant cellular machinery to influence growth and development. Recent evidence strongly suggests that plant cells have plasma membrane receptors with intrinsic protein kinase activity. The plant receptor-like protein kinases (RLK) are structurally related to the animal polypeptide growth factor receptors; however, the plant RLKs all appear to be serine/threonine protein kinases. Diversity among plant RLKs, reflected in their structural and functional properties, has opened up a broad new area of investigation into cellular signaling in plants with far-reaching implications for the mechnaisms by which plant cells perceive and respond to extracellular stimuli. Our specific aims are to characterize the biochemical properties, both in vitro and in vivo, of one receptor-like protein kinase (RLK5) from Arabidopsis thaliana. We have shown that a recombinant fusion protein of this transmembrane protein kinase will autophosphorylate several sites and that autophosphorylation is critical for interaction with cellular targets. The work will now further investigate the nature of the autophosphorylation and how it is important in the signaling sequence of events. It is anticipated that results from these studies will yield fundamental and new insights into the molecular mechanisms of how plants perceive their environment and how growth and developmental processes are regulated by environmental signals. ***
