2 GENES THAT ENCODE CA2-DEPENDENT PROTEIN-KINASES ARE INDUCED BY DROUGHT AND HIGH-SALT STRESSES IN ARABIDOPSIS-THALIANA()

Two cDNA clones, cATCDPK1 and cATCDPK2, encoding Ca2+-dependent, calmo dulin-independent protein kinases (CDPK) were cloned from Arabidopsis thaliana and their nucleotide sequences were determined. Northern blot analysis indicated that the mRNAs corresponding to the ATCDPK1 and AT CDPK2 genes are rapidly induced by drought and high-salt stress but no t by low-temperature stress or heat stress. Treatment of Arabidopsis p lants with exogenous abscisic acid (ABA) had no effect on the inductio n of ATCDPK1 or A TCDPK2. These findings suggest that a change in the osmotic potential of the environment can serve as a trigger for the in duction of ATCDPK1 and ATCDPKZ. Putative proteins encoded by ATCDPK1 a nd ATCDPK2 which contain open reading frames of 1479 and 1488 bp, resp ectively, are designated ATCDPK1 and ATCDPK2 and show 52% identity at the amino acid sequence level. ATCDPK1 and ATCDPK2 exhibit significant similarity to a soybean CDPK (51% and 73%, respectively). Both protei ns contain a catalytic domain that is typical of serine/ threonine pro tein kinases and a regulatory domain that is homologous to the Ca2+-bi nding sites of calmodulin. Genomic Southern blot analysis suggests the existence of a few additional genes that are related to ATCDPK1 and A TCDPK2 in the Arabidopsis genome. The ATCDPK2 protein expressed in Esc herichia coli was found to phosphorylate casein and myelin basic prote in preferentially, relative to a histone substrate, and required Ca2for activation.