Identification and expression analyses of calmodulin-binding transcription activator genes in soybean

Environmental stresses are major hurdles for the production of soybean (Glycine max), a major food crop that is able to acquire N and P nutrients through symbiotic association with rhizobia and arbuscular mycorhizal fungi. The calmodulin-binding transcription activators (CAMTA) belong to a transcription factor family that plays critical roles in plant responses to both abiotic and biotic stresses such as drought, cold and attacks from pathogens and insects. Our current knowledge about CAMTA genes in soybean is scarce, but is of critical significance to the improvement of stress tolerance and production of soybean, a worldwide major protein-rich food crop. In this study, we first searched for all the CAMTA homologous genes in the whole genome of soybean. We then surveyed the distribution of stress-related cis-regulatory elements in the -1.5 kb promoter regions of all GmCAMTA genes. Next, we analyzed the expression patterns of all these GmCAMTAs in root and leaf tissues and studied how they respond to various stress treatments by quantitative RT-PCR. Fifteen genes in the soybean genome were identified to encode CAMTA proteins, and their gene structures and protein sequences were highly similar to that in Arabidopsis. Like their counterparts in other plants and animals, all GmCAMTAs contain a CG-1 DNA-binding domain in the N terminal region, followed by a TIG domain, ankyrin repeats, IQ motifs and a calmodulin binding site. All GmCAMTA genes were found to be expressed in root and leaf tissues. The expression of all GmCAMTAs was induced by salinity. Most of the GmCAMTA genes were induced by several stresses and hormone signals including dehydration, cold, H2O2, abscisic acid, salicylic acid, and methyl jasmonate. Only four GmCAMTAs (GmCAMTA5, 6, 7 and 10) were found to be repressed by H2O2 treatment. Consistent with their responsiveness to all these stimuli, many stress-related cis-elements were found in the promoter regions of all the GmCAMTA genes. These results indicate that GmCAMTA genes are responsive to various stress and hormone signals, and likewise, GmCAMTAs could act as critical components in regulating soybean tolerances to various environmental stresses.