| Summary: | <p>Abstract</p> <p>Background</p> <p>In plants, a large family of calmodulin (CaM) and CaM-like (CML) proteins transduce the increase in cytosolic Ca<sup>2+</sup> concentrations by binding to and altering the activities of target proteins, and thereby affecting the physiological responses to a vast array of stimuli. Here, transcript expression analysis of <it>Cam</it> and <it>CML</it> gene family members in rice (<it>Oryza sativa</it> L.) was extensively examined.</p> <p>Results</p> <p><it>Cam</it> and <it>CML</it> genes in rice exhibited differential expression patterns in tissues/organs. Under osmotic stress and salt stress, expression of <it>OsCam1-1</it>, <it>OsCML4</it>, <it>5</it>, <it>8</it>, and <it>11</it> was induced with different kinetics and magnitude. <it>OsCML4</it> and <it>8</it> mRNA levels significantly increased by 3 h after treatment and remained elevated for at least 24 h while expression of <it>OsCam1-1</it>, <it>OsCML5</it> and <it>11</it> was up-regulated as early as 1–3 h before rapidly returning to normal levels. Several <it>cis</it>-acting elements in response to abiotic stresses, including DREs (important promoter elements responsive to drought, high salt, and cold stress), were detected in the 5<sup>′</sup> upstream regions of these genes. The observed induction of the GUS activity of transgenic rice plants via the <it>OsCam1-1</it> promoter appeared to be biphasic and dependent on the severity of salt stress.</p> <p>Conclusions</p> <p>Large <it>OsCam</it> and <it>OsCML</it> gene family members likely play differential roles as signal transducers in regulating various developmental processes and represent important nodes in the signal transduction and transcriptional regulation networks in abiotic stresss responses mediated by the complex Ca<sup>2+</sup> signals in plants, which are rich in both spatial and temporal information.</p>
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