Effect of the HCT Gene on Lignin Synthesis and Fiber Development in Gossypium barbadense

As one of the key enzymes in the metabolic pathway of phenylpropane, shikimate hydroxycinnamoyl transferase (HCT) is mainly involved in the biosynthesis of the plant secondary cell wall, which is closely related to cotton fiber quality. In this study, whole-genome identification and bioinformatics analysis of the HCT gene family were performed in G. barbadense. In the whole genome, we identified 136 GbHCT genes encoding 309-504 amino acids. Phylogenetic analysis divided the genome into 5 subfamilies, which were located on 25 chromosomes. Collinear analysis of polyploidization and tandem duplication events were the main driving forces for the rapid expansion and evolution of this family, and the genes underwent loose purifying selection constraints after duplication. Gene promoters identified a variety of cis-acting elements related to plant hormones and the stress response. Several members of the GbHCT family were highly expressed during the development of cotton fiber, and different members had different expression patterns in cotton fiber. After GbHCT114 gene silencing in cotton, the amount of stem surface trichomes and lignin content decreased, and the cell morphology and arrangement changed. After the GbHCT114 gene was overexpressed in Arabidopsis thaliana (L.) Heynh., the number of stem and leaf surface trichomes and the cross-sectional area of the secondary xylem duct cell wall increased. In addition, utilizing transcriptomic analysis, differentially expressed genes associated with lignin synthesis and fiber development were identified. Taken together, the results obtained in this study confirm that the GbHCT114 gene regulates plant trichome development, which lays a theoretical foundation for future studies on the function of GbHCT114 in cotton.