Identification and expression of calmodulin genes and involvement in salt stress response in rice Oryza sativa L.

Abstract

A wide range of stimuli evoke transient increases of different magnitude and specialized characteristics in [Ca2+ ]cyt, which are typically transmitted by protein sensors that contain Ca2+ - binding EF-hand motifs. Ca2+ -binding results in conformation changes that modulate their activity or ability to interact with other proteins. By functional analyses and BLAST searches of the TIGR database, a maximum number of 243 proteins that possibly have EF-hand motifs were identified in the Oryza sativa L. genome. Using a neighbor-joining tree based on amino acid sequence similarity, a group of 37 Oryza sativa L. genes encoding calmodulin (CaM) and related proteins that do not possess functional domains other than the Ca2+ - binding EF-hand motifs was identified of which five loci of Cam genes and 32 genes coding for CaM-like (CML) proteins were defined. Extensive analyses of the gene structures, the chromosome locations, the EF-hand motif organization, expression chatacteristics and comparative analysis of Cam and CML genes in rice and Arabidopsis are presented. By RT-PCR, each of the five OsCam and OsCML1 gene were shown to express in leaves, roots, flowers, seeds and calli. Examination of Cam genes under salt stress by RNA gel blot analysis indicates that OsCam1-1 expression was strongly induced at 0.5-1 hr followed by a decrease thereafter. In contrast, the mRNA levels of other Cam genes are relatively unchanged under salt stress. The expression patterns of OsCam1-1 were further examined in KDML105 in comparison with FL530, a KDML 105-derived salt-tolerant line. In leaves, expression of OsCam1-1 gene was induced by salt stress whereas the salt stress did not increase its mRNA level in roots of both lines. In addition, effects of exogenous Abscisic acid (ABA) applied two hours before salt stress treatment were investigated. As a result, ABA did not have an effect on the induction by salt stress in FL530 leaves and appeared to bounter the effect of OsCam1-1 induction in leaves of KDML105. Conversely, ABA increased the expression of OsCam1-1 gene in roots of both lines which suggests its possible role in mediating ABA actions in roots. However, the induction in FL530 occurred to a lesser extend without salt stress treatment and was prolonged under salt stress treatment, which suggests that OsCam1-1 gene probably has an important role in salt stress response mediated by ABA.