DREB2 (dehydration-responsive element-binding protein 2) type transcription factor in sorghum (Sorghum bicolor): genome-wide identification, characterization and expression profiles under cadmium and salt stresses.

Biotic and abiotic stresses negatively affect fitness, biomass production, and crop yield in plants. The dehydration-responsive element-binding proteins (DREB) are important transcription factors (TFs), and are induced by abiotic and biotic stresses. In this study, genome-wide identification, in silico sequence, and phylogenetic analyses and expression analyses of DREB2 genes under cadmium (Cd) and salt (NaCl) stresses in sorghum (Sorghum bicolor, Sb) were performed. Six putative SbDREB2 genes were identified in sorghum genome and all contained AP2 domain (PF00847). Nucleotide diversities in SbDREB2 genes were calculated as π: 0.53 and θ: 0.39, respectively. While exon numbers of them were either one or two, length of SbDREB2 proteins ranged from 238 to 388 amino acid residues. Fifty-six cis-acting regulatory elements, which are tissue specific, light, hormone, and stress responsive, were identified in the promotor regions of SbDREB2 genes. Analyses on digital expression data indicated that SbDREB2A and SbDREB2B are more expressed genes than other SbDREB genes in sorghum. Under Cd and NaCl stresses, expressions of SbDREB2 genes were induced at different levels. All SbDREB2 genes in root were up-regulated under salt stress. In case of Cd stress, SbDREB2D gene was particularly up-regulated in leaves and roots. Co-expression analyses revealed four of TFs in co-expression network, indicating that they have roles in transcriptional cascade. Furthermore, five miRNA target regions were identified for four SbDREB2 genes, indicating their roles in post-transcriptional regulation. The predicted 3D structure of SbDREB2 proteins showed some structural divergences and structure overlap between rice and sorghum varied at between 26.58 and 50%. Finally, obtained data could be used in breeding of stress-tolerant plants, particularly genetically engineered DREB2 expressing plants. Findings in this study would also contribute to the understanding of DREB2 genes in plants, especially in sorghum.