Genome-wide identification of the MIOX gene family and their expression profile in cotton development and response to abiotic stress.

The enzyme myo-inositol oxygenase (MIOX) catalyzes the myo-inositol into glucuronic acid. In this study, 6 MIOX genes were identified from all of the three diploid cotton species (Gossypium arboretum, Gossypium herbaceum and Gossypium raimondii) and Gossypioides kirkii, 12 MIOX genes were identified from two domesticated tetraploid cottons Gossypium hirsutum, Gossypium barbadense, and 11 MIOX genes were identified from three wild tetraploid cottons Gossypium tomentosum, Gossypium mustelinum and Gossypium darwinii. The number of MIOX genes in tetraploid cotton genome is roughly twice that of diploid cotton genome. Members of MIOX family were classified into six groups based on the phylogenetic analysis. Integrated analysis of collinearity events and chromosome locations suggested that both whole genome duplication and segmental duplication events contributed to the expansion of MIOX genes during cotton evolution. The ratios of non-synonymous (Ka) and synonymous (Ks) substitution rates revealed that purifying selection was the main force driving the evolution of MIOX genes. Numerous cis-acting elements related to light responsive element, defense and stress responsive element were identified in the promoter of the MIOX genes. Expression analyses of MIOX genes based on RNA-seq data and quantitative real time PCR showed that MIOX genes within the same group shared similar expression patterns with each other. All of these results provide the foundation for further study of the biological functions of MIOX genes in cotton environmental adaptability.