REQUIREMENT FOR THE INDUCED EXPRESSION OF A CELL-WALL ASSOCIATED RECEPTOR KINASE FOR SURVIVAL DURING THE PATHOGEN RESPONSE

Pathogen infection of angiosperms must rely on some interaction betwee n the extracellular matrix (ECM) and the invading agent, and may be ac companied by signaling between the ECM and cytoplasm. An Arabidopsis c ell wall associated receptor kinase (Wak1) has an amino-terminal domai n that is tightly associated with the ECM, spans the plasma membrane a nd has a cytoplasmic protein kinase domain. Wak1 expression is induced when Arabidopsis plants are infected with pathogen, or when the patho gen response is stimulated either by exogenous salicylate (SA) or its analog 2,2-dichloroisonicotinic acid (INA). This Wak1 induction requir es the positive regulator NPR1/NIM1. Thus Wak1 is a pathogen-related ( PR) protein. Expression of an antisense and a dominant negative allele of Wak1 shows that induced expression of Wak1 is needed for a plant t o survive if stimulated by INA. Ectopic expression of the entire Wak1, or the kinase domain alone, can provide resistance to otherwise letha l SA levels. These experiments suggest that Wak1 expression and other PR proteins are protecting plants from detrimental effects incurred du ring the pathogen response. These results provide a direct link betwee n a protein kinase that could mediate signals from the ECM, to the eve nts that are precipitated by a pathogen infection.