Genome-wide identification and characterization of the C2 domain family in Sorghum bicolor (L.) and expression profiles in response to saline–alkali stress

The C2 domain family proteins in plants has been recently shown to be involved in the response to abiotic stress such as salt and drought stress. However, less information on C2 domain family members has been reported in Sorghum bicolor (L.), which is a tolerant cereal crop. To elaborate the mechanism of C2 domain family members in response to abiotic stress, bioinformatic methods were used to analyze this family. The results indicated that 69 C2 domain genes belonging to 5 different groups were first identified within the sorghum genome, and each group possessed various gene structures and conserved functional domains. Second, those C2 family genes were localized on 10 chromosomes 3 tandem repeat genes and 1 pair of repeat gene fragments were detected. The family members further presented a variety of stress responsive cis-elements. Third, in addition to being the major integral component of the membrane, sorghum C2 domain family proteins mainly played roles in response to abiotic and biotic stress with their organic transport and catalytic activity by specific location in the cell on the basis of gene ontology analysis. C2 family genes were differentially expressed in root, shoot or leaf, and shown different expression profiling after saline–alkali stress, which indicated that C2 family members played an important role in response to saline–alkali stress based on the transcription profiles of RNA-seq data and expression analysis by quantitative real-time polymerase chain reaction. Besides, most C2 family members were mainly located in cytoplasmi and nucleus. Weighted gene co-expression network analysis revealed three modules (turquoise, dark magenta and pink) that were associated with stress resistance, respectively. Therefore, the present research provides comprehensive information for further analysis of the molecular function of C2 domain family genes in sorghum.