Genome-wide analysis of HSP70 superfamily in Gossypium raimondii and the expression of orthologs in Gossypium hirsutum

Heat shock 70 (HSP70) proteins are highly conserved molecular chaperones widely existed in the plant kingdom which are involved in cellular protein folding process. In this study, comprehensive evolutionary analyses of the Gossypium raimondii HSP70 gene family members are conducted and 30 HSP70 genes are identified. The gene structure, chromosome distribution, gene duplication and phylogenic evolution of this family are further analyzed. The results reveal that HSP70 family genes can be clustered into several major subgroups based on their sub-cellular locations, and the gene structures are relatively conserved in each subgroup. Both tandem duplications and chromosome segmental duplications are found to contribute to the expansion of HSP70 gene family. Evolutionary analysis of HSP70s in diverse species reveals that the differentiation of HSP70 subgroups occurred before the multi-cell and single-cell differentiation, with the cytoplasmic HSP70s multiple amplified. The expression pattern of HSP70 genes under series of fiber development stages indicates that many HSP70 genes may participate in fiber development processes including fiber initiation and elongation. This study provides the complete profiles of cotton HSP70 family genes for future study on their functions related to the molecular mechanisms of fiber development.