Expression of rice Ca2+-dependent protein kinases (CDPKs) genes under different environmental stresses

Ca2+-dependent protein kinases (CDPKs) play an essential role in plant Ca2+-mediated signal transduction. Twenty-nine CDPK genes have been identified in the rice genome through a complete search of genome and full-length cDNA databases. Eight of them were reported previously to be inducible by different stress stimuli. Sequence comparison revealed that all 29 CDPK genes (OsCPK1-29) contain multiple stress-responsive cis-elements in the promoter region (1 kb) upstream of genes. Analysis of the information extracted from the Rice Expression Database indicates that 11 of the CDPK genes are regulated by chilling temperature, dehydration, salt, rice blast infection and chitin treatment. RT-PCR and RNA gel blot hybridization were performed in this study to detect the expression 19 of the CDPK genes. Twelve CDPK genes exhibited cultivar- and tissue-specific expression; four CDPK genes (OsCPK6, OsCPK13, OsCPK17 and OsCPK25) were induced by chilling temperature, dehydration and salt stresses in the rice seedlings. While OsCPK13 (OsCDPK7) was already known to be inducible by chilling temperature and high salt, this is the first report that the other three genes are stress-regulated. OsCPK6 and OsCPK25 are up-regulated by dehydration and heat shock, respectively, while OsCPK17 is down-regulated by chilling temperature, dehydration and high salt stresses. Based on this evidence, rice CDPK genes may be important components in the signal transduction pathways for stress responses. Findings from this research are important for further dissecting mechanisms of stress response and functions of CDPK genes in rice.