MOLECULAR-CLONING OF 2 NOVEL RICE CDNA SEQUENCES ENCODING PUTATIVE CALCIUM-DEPENDENT PROTEIN-KINASES

We have isolated, from a cDNA library constructed from rice coleoptile s, two sequences, OSCPK2 and OSCPK11, that encode for putative calcium -dependent protein kinase (CDPK) proteins. OSCPK2 and OSCPK11 cDNAs ar e related to SPK, another gene encoding a rice CDPK that is specifical ly expressed in developing seeds [20]. OSCPK2 and OSCPK11-predicted pr otein sequences are 533 and 542 amino acids (aa) long with a correspon ding molecular mass of 59436 and 61079 Da respectively. Within their p olypeptide chain, they all contain those conserved features that defin e a plant CDPK; kinase catalytic sequences are linked to a calmodulin- like regulatory domain through a junction region. The calmodulinlike r egulatory domain of the predicted OSCPK2 protein contains 4 EF-hand ca lcium-binding sites while OSCPK11 has conserved just one canonical EF- hand motif. In addition, OSCPK2- and OSCPK11-predicted proteins contai n, at their N-terminal region preceding the catalytic domain, a stretc h of 80 or 74 residues highly rich in hydrophilic amino acids. Compari son of the NH2-terminal sequence of all three rice CDPKs so far identi fied (OSCPK2, OSCPK11 and SPK) indicates the presence of a conserved M GxxC(S/Q)xxT motif that may define a consensus signal for N-myristoyla tion. OSCPK2 and OSCPK11 proteins are both encoded by a single-copy ge ne and their polyadenylated transcripts are 2.4 and 3.5 kb long respec tively. OSCPK2 and OSCPK11 mRNAs are equally abundant in rice roots an d coleoptiles. A 12 h white light treatment of the coleoptiles reduces the amount of OSCPK2 mRNA with only a slight effect on the level of O SCPK11 transcript. With anoxic treatments, OSCPK2 mRNA level declined significantly and promptly while the amount of OSCPK11 transcript rema ined constant.