Genome-wide identification and characterization of terpene synthase genes in Gossypium hirsutum

Terpenoids are widely distributed in plants and play important roles in the regulation of plant growth and development and in the interactions between plants and both the environment and other organisms. However, terpene synthase (TPS) genes have not been systematically investigated in the tetraploid Gossypium hirsutum. In this study, whole genome identification and characterization of the TPS family from G. hirsutum were carried out. Eighty-five TPS genes, including 47 previously unidentified genes, were identified in the G. hirsutum genome and classified into 5 subfamilies according to protein sequence similarities, as follows: 43 GhTPS-a, 29 GhTPS-b, 4 GhTPS-c, 7 GhTPS-e/f, and 2 GhTPS-g members. These 85 TPS genes were mapped onto 19 chromosomes of the G. hirsutum genome. Segmental duplications and tandem duplications contributed greatly to the expansion of TPS genes in G. hirsutum and were followed by intense purifying selection during evolution. Indentification of cis-acting regulatory elements suggest that the expression of TPS genes is regulated by a variety of hormones. RNA sequencing (RNA-seq) expression profile analysis revealed that the TPS genes had distinct spatiotemporal expression patterns, and several genes were highly and preferentially expressed in the leaves of cotton with gossypol glands (glanded cotton) versus a glandless strain. Virus-induced gene silencing (VIGS) of three TPS genes yielded plants characterized by fewer, smaller, and lighter gossypol glands, which indicated that these three genes were responsible for gland activity. Taken together, our results provide a solid basis for further elucidation of the biological functions of TPS genes in relation to gland activity and gossypol biosynthesis to develop cotton cultivars with low cottonseed gossypol contents.