A Cell Wall Associated, Receptor Like Kinase

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Iohorn 9603703 Technical We have identified a family of Arabidopsis thaliana proteins, designated Waks for Wall Associated Kinase, that are tightly associated with the cell wall, and that have cytoplasmic kinase domains. The cell wall bound, extracytoplasmic domain of each family member contains several Epidermal Growth Factor (EGF) repeats. Waks differ, however, in the extracellular domain . In different 100 amino acid blocks one Wak has 54% identity (perfect spacings) to tenascin. In another there is identity with a neurexin and in another there identity with extensin. The Wak family is expressed in all vegetative tissues of Arabidopsis, and has relatives in other Angiosperms. Based on immunoelectron microscopy and biochemical analysis, Waks provides a physical continuum between the cell wall and the cytoplasm. Since the kinase is cytoplasmic it also has the potential to mediate signals to the cytoplasm from the cell wall. Indeed, we find that at least one Wak interacts with a cytoplasmic type 2C protein phosphatase that is likely the first step in the transduction pathway. Future experiments will focus on the genomic organization and specific expression of each family member, and their interaction with each other and cytoplasmic proteins. We have isolated a T-DNA disruption of the Wak locus that is tightly linked to an embryonic lethal phenotype, and we plan to use this mutant background to assay functional domains of the Waks. Moreover, expression of dominant negative Wak mutations also show that the family is essential for viability, and genetic screens will be used to identify interacting proteins. Non-Technical Extrinsic signals impinging upon plant cells first interact with the cell wall that surrounds the cell. Many of these extrinsic signals induce overt alterations in a plant's physiology and morphology. The site of detection of these most of these signals is unknown. Dr. Kohorn has discovered a class of signaling proteins (cell-wall associated kinase or Wak) that app ear to be associated with the inner surface of the cell wall directly adjacent to the cell surface. With this award Dr. Kohorn will characterize the genes encoding Wak and to examine how Wak interacts with other proteins to create a coupled cascade where signals perceived by Wak are transmitted into the cell to exert physiological effects. ***