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Kissing Cousins: Calcium-Regulated and UnRegulated Kinases in the CDPK/SnRK Family of Protein kinases in Arabidopsis.   Alice C. Harmon, Dept. of Botany and the Program in Plant Molecular and Cellular Biology, Univ. of Florida.

   The CDPK/SnRK family of protein kinases is comprised of 84 members, 59 of which are thought to be regulated by calcium. The CDPKs (calcium-dependent protein kinases or calmodulin-like domain protein kinases) are directly regulated by the binding of calcium to a regulatory domain located at the C-terminus of these proteins. In contrast, members of subgroup 3 of the SNF1-related kinases (SnRK3) are regulated by the binding of calcium to a separate protein, which in turn binds to the kinase. The remaining 25 family members are divided among five groups: CDPK-related kinases (CRKs), PEP-Carboxylase kinases (PPCKs), PPCK-Related kinases (PEPRKs), SnRK1s, and SnRK2s. While these latter kinases are not regulated by calcium, they may overlap in substrate specificity with the calcium-regulated kinases. Current evidence indicates that family members play roles in the regulation of metabolism and gene expression in response to environmental and developmental cues.

   In a collaborative Arabidopsis 2010 research project, we are examining the function of 64 members of the CDPK/SnRK family. To identify substrates and interacting proteins, yeast-two hybrid screens are being performed with substrate-trap constructs. Results from a screen with CPK4 have revealed several potential substrates, and screens with PPCKs 1 and 2 are in progress. The substrate specificity of family members is being determined by mapping the phosphorylation sites of Arabidopsis proteins phosphorylated by the kinases in vitro. We are also determining the subcellular location of GFP-tagged constructs of the kinases. Preliminary results indicate that various CPKs are located in the cytoplasm, plasma membrane, endoplasmic reticulum, or with peroxisomes.

(Supported by NSF MCB 0114769 to ACH et al. and DBI-9975808 to J.C. Walker et al.)

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