A CELL WALL-ASSOCIATED, RECEPTOR-LIKE PROTEIN-KINASE

Physical connections between higher plant cell walls and the plasma me mbrane have been identified visually, but the molecules involved in th e contact are unknown. We describe here an Arabidopsis thaliana protei n kinase, designated Wak1 for wall-associated kinase, whose predicted extracytoplasmic domain contains several epidermal growth factor repea ts and identity with a viral movement protein. Wak1 fractionates with insoluble material when plant tissue is ground in a variety of buffers and detergents, suggesting a tight association with the plant extrace llular matrix. Immunocytochemistry confirms that Wak1 is associated wi th the cell wall. Enzymatic digestion of the cell wall allows the rele ase of Wak1 from the insoluble cell wall fraction, and protease experi ments indicate that Wak1 likely has a cytoplasmic kinase domain, and t he EGF containing domain is extracellular. Wak1 is found in all vegeta tive tissues of Arabidopsis, and has relatives in other angiosperms, b ut not Chlamydomonas. We suggest that Wak1 is a good candidate for a p hysical continuum between the cell wall and the cytoplasm, and since t he kinase is cytoplasmic, it also has the potential to mediate signals to the cytoplasm from the cell wall.