Genome-wide identification, characterization and expression analysis of the expansin gene family under drought stress in tea (Camellia sinensis L.)

During several developmental processes, expansins contribute to cell enlargement by promoting cell wall loosening. To explore the biological roles of expansins during drought stress response and to characterize different expansins in tea, we performed a detailed analysis of the expansin gene family covering phylogeny, gene structure, profiling of gene expression and co-expression network analysis. We identified a total of 40 expansin genes in the tea genome belonging to 3 subfamilies, out of which 29 tea expansins belong to EXPA, 9 to EXLA and 2 to EXPB subfamilies. A minimum of 3 and a maximum of 13 exons are present in the gene structure of expansins. Presence of drought stress responsive cis-acting elements in the upstream of promoter regions of 40% of the identified expansins shows that the putative expansins may have been involved in tea plant's response to drought stress. At least 15 out of the 40 expansin genes are found to be differentially expressed in response to drought in each of the drought stress related public datasets analysed in-silico. TEA022767 belonging to EXPA subfamily is seen to be upregulated during drought stress, as revealed from the analysis of all three publicly available bio-projects. Co-expression network analysis shows that TEA022767 and TEA032954 form a connecting link between two expression correlation groups that further signifies their role in drought stress response in tea. This study helps to interpret and to understand the biological roles of diverse expansin genes in tea plants under drought stress conditions.