Evolution and Stress Responses of Gossypium hirsutum SWEET Genes.

The SWEET (sugars will eventually be exported transporters) proteins are sugar efflux transporters containing the MtN3_saliva domain, which affects plant development as well as responses to biotic and abiotic stresses. These proteins have not been functionally characterized in the tetraploid cotton, , which is a widely cultivated cotton species. In this study, we comprehensively analyzed the cotton gene family. A total of 55 putative genes were identified. The genes were classified into four clades based on a phylogenetic analysis and on the examination of gene structural features. Moreover, chromosomal localization and an analysis of homologous genes in , , and suggested that a whole-genome duplication, several tandem duplications, and a polyploidy event contributed to the expansion of the cotton gene family, especially in Clade III and IV. Analyses of -acting regulatory elements in the promoter regions, expression profiles, and artificial selection revealed that the genes were likely involved in cotton developmental processes and responses to diverse stresses. These findings may clarify the evolution of gene family and may provide a foundation for future functional studies of SWEET proteins regarding cotton development and responses to abiotic stresses.