Genome-wide identification of the Gossypium hirsutum CAD gene family and functional study of GhiCAD23 under drought stress.

Cinnamyl alcohol dehydrogenase (CAD) is a crucial enzyme in the final stage of lignin monomer biosynthesis. This study focuses on the CAD gene family within Gossypium hirsutum. Through comprehensive genomic analysis, we identified 29 GhiCAD genes within the Gossypium hirsutum genome using a bioinformatics approach. Phylogenetic analysis revealed that the GhiCAD family can be categorized into four subgroups, which are closest to the evolutionary relationship with Arabidopsis thaliana. There are multiple cis-acting elements on the promoters of GhiCAD genes associated with abiotic stress responses. Some GhiCAD genes demonstrated high expression in various tissues like root, leaf, and sepal, as well as in fiber and ovule at different developmental stages (10 days post anthesis (DPA), 15 DPA, 20 DPA, 25 DPA). The transcript levels of GhiCAD23 were notably elevated when exposed to PEG treatment and drought stress (DS). GhiCAD23 is also co-expressed with many known drought response genes, suggesting its involvement in the plant's reaction to DS. Employing virus-induced gene silencing (VIGS) technology to silence the GhiCAD23 gene, it was found that silencing GhiCAD23 reduced the tolerance of cotton to DS. Under DS, the relative leaf water content, superoxide dismutase (SOD), and catalase (CAT) enzyme activities of the GhiCAD23-silenced cotton plants were decreased by 31.84%, 30.22% and 14.19%, respectively, while malondialdehyde (MDA) was increased by 72.16% compared with the control cohort. Drought promotes the accumulation of lignin, and it was found that silencing the GhiCAD23 reduces lignin accumulation in cotton under DS. The analysis of phenotypic and physiological indicators indicates that GhiCAD23 is vital in cotton's resistance to DS. This investigation provides an important reference for future comprehensive exploration of the GhiCAD23 gene's function in cotton's DS response mechanism.