Genome-wide identification and functional analysis of TCX gene family and the critical role of GhTCX17 in response to drought and salt stress in cotton.

Cotton is an important natural fiber crop. The Tesmin/TSO1-like CXC (TCX) gene family plays an important role in plant resistance to environmental stress, and its mechanism is still not clear in cotton. In this study, we systematically identified the potential functions of TCX family genes in cotton were investigated based on genome identification, phylogenetic and genomic analyses, chromosome mapping and cis-regulatory element prediction. A total of 79 TCX genes were identified in the genome-wide analysis of four cotton species. Chromosomal localization and synteny analysis revealed that the TCX gene family was relatively conservative and fragment replication was the main amplification mode of TCX gene family during cotton evolution. Cis-element analysis showed that there were a plenty of elements related to light response, hormone response and abiotic stress response in the TCX gene promoter. Gene expression analysis based on RNA-seq and qRT-PCR showed that TCX genes were responsive to abiotic stress. The key gene GhTCX17 was cloned for functional verification. GhTCX17 protein was localized in the nucleus. Under drought and salt stress, silencing GhTCX17 gene plants showed leaf wilting aggravation, decreased total antioxidant capacity, increased malondialdehyde content compared with control plants, implied the reducing drought and salt tolerance of silencing GhTCX17 gene in cotton. This study revealed the evolution and function diversity of the TCX gene family and laid an important foundation for further study to dissect TCX gene family functioning mechanisms on cotton stress resistance.