Calcium signaling-mediated and differential induction of calmodulin gene expression by stress in Oryza sativa L.

Ca2+/calmodulin transduction pathways have been implicated in mediating stress response and tolerance in plants. Here, three genes encoding calmodulin (Cam) members of the EF-hand family of Ca2+-binding proteins were identified from Oryza saliva L. databases. Complementary DNA for each of the calmodulin genes, OsCam1, OsCam2, and OsCam3 were sequenced. OsCam1 and OsCan2 encode a conventional 148-amino acid calmodulin protein that contains four characteristic Ca2+-binding motifs. OsCam3 encode a similar protein with a 38-amino-acid extension containing a putative prenylation site (CVIL) at the carboxyl terminus. RT-PCR showed that each of the genes is expressed in leaves and roots of 2-week old rice seedlings. By RNA gel blot analysis, OsCam1 mRNA levels strongly increased in response to NaCl, mannitol and wounding treatments. In contrast, OsCam2 mRNA levels were relatively unchanged under all conditions investigated. NaCl treatment and wounding also increased the OsCam3 mRNA level, but in a more transient manner. Our results indicate that although the expression of genes encoding different calmodulin isoforms is ubiquitous, they are differentially regulated by various stress signals. In addition, we have demonstrated that the calcium-channel blocker lanthanum chloride inhibited the induction of OsCam1 gene expression by both NaCl and mannitol treatments. These results suggest that osmotic stress-induced expression of OsCam1 gene requires the [Ca2+](cyt) elevation that is known to occur in response to these stimuli.