Minisymposium 6: Intercellular Signaling

Abs # 16002: Analysis of a knockout mutant for a cell wall associated receptor kinase reveals its role in Arabidopsis heavy metal responses

Presenter:	Jackson, Angela , zhe@sfsu.edu
Authors	Jackson, Angela  (A)   Verica, Joseph A. (A)   Tong, Hongyun  (A)   Chae, Lee  (A)   Selby, Jessie  (A)   He, Zheng-Hui  (A)
Affiliations:	(A): Department of Biology, San Francisco State University, 1600 Holloway Ave., San Francisco, CA 94132 USA
Web Site:	http://userwww.sfsu.edu/~zhe/

A family of genes with sequence similarity to the cell wall-associated kinase (WAK) genes in Arabidopsis has recently been identified (Verica, J. and He, Z.-H., Plant Physiology 129:455-459, 2002). The WAKs represent a unique class of receptor-like kinase genes. Each encodes a transmembrane protein with a cytoplasmic serine/threonine kinase domain and an extracellular region with similarity to vertebrate epidermal growth factor (EGF)-like domains. The WAKs and the WAK-like kinases (WAKLs) are good candidates for signaling molecules that may physically link the cell wall to the cytoplasm of a plant cell. WAK/WAKL proteins thus may play important roles in cell-cell and cell-environment communications. Our previous molecular and genetic studies have shown that WAK genes are required for various cellular processes including pathogenesis and cell elongation (He et al., Plant J. 14:55-63,1998; Lally et al., Plant Cell 13:1317-1331, 2001). In this study, the functional roles for one of the newly discovered WAKL members, WAKL14, were examined. E. coli expressed WAKL14 protein has auto-phosphorylation activities suggesting WAKL14, as predicted, encodes an active kinase. The WAKL14 antibody localized WAKL14 protein to the cell surface suggesting, like other WAK proteins, WAKL14 may also serve as a plasma membrane-localized receptor kinase. WAKL14 promoter-GUS analyses revealed that WAKL14 expression are responding to various abiotic stresses. The WAKL14 expression in root tips is highly up-regulated when roots are exposed to 80 µM Zn, Ni or Cu. A T-DNA knockout mutant for WAKL14 was isolated. Southern and northern analyses showed that the isolated wakl14 mutant carries a WAKL14 null mutation. Analyses for the wakl14 mutant on media containing various heavy metals have revealed the wakl14 mutant is hypersensitive to heavy metals including zinc and nickel. In the presence of these heavy metals, Arabidopsis growth and development in the wakl14 mutant, as measured by root/lateral root elongation and biomass accumulation, are reduced by more than 25% when compared to that in the wild type. Based on our biochemical, molecular and genetic analyses of WAKL14, we conclude that WAKL14 gene encodes a receptor kinase that may play an important role in Arabidopsis heavy metal responses.