Interaction of the arabidopsis receptor protein kinase Wak1 with a glycine-rich protein, AtGRP-3

The Arabidopsis wall-associated receptor kinase, Wak1, is a member of the W ak family (Wak1-5) that links the plasma membrane to the extracellular matr ix, By the yeast two-hybrid screen, we found that a glycine-rich extracellu lar protein, AtGRP-3, binds to the extracellular domain of Wak1, Further in vitro binding studies indicated that AtGRP-3 is the only isoform among the six tested AtGRPs that specifically interacts with Waks, and the cysteine- rich carboxyl terminus of AtGRP-3 is essential for its binding to Wak1, We also show that Wak1 and AtGRP-3 form a complex with a molecular size of sim ilar to 500 kDa in vivo in conjunction with the kinase-associated protein p hosphatase, KAPP, that has been shown to interact with a number of plant re ceptor-like kinases, Binding of AtGRP-3 to Wak1 is shown to be crucial for the integrity of the complex. Wak1 and AtGRP-3 are both induced by salicyli c acid treatment. Moreover, exogenously added AtGRP-3 up-regulates the expr ession of Wak1, AtGRP-3, and PR-1 (for (p) under bar athogenesis-(r) under bar elated) in protoplasts. Taken together, our data suggest that AtGRP-3 r egulates Wak1 function through binding to the cell wall domain of Wak1 and that the interaction of Wak1 with AtGRP-3 occurs in a pathogenesis-related process in planta.