Overexpression of GhCAD6 in Upland Cotton (Gossypium hirsutum L.) Enhances Fiber Quality and Increases Lignin Content in Fibers

Cotton is a vital economic crop, and cotton fiber serves as the primary raw material for the textile industry. Lignin in cotton fiber is closely associated with fiber quality. Lignin is synthesized through the phenylpropanoid metabolic pathway, where the cinnamyl alcohol dehydrogenase gene <i>CAD6</i> plays a significant role. In this study, we obtained successfully transformed overexpression plants by constructing an overexpression vector and performing genetic transformation and tissue culture. To verify the function of the <i>GhCAD6</i> gene in upland cotton, we analyzed the agronomic traits, fiber quality, cell wall structure, and lignin content of <i>GhCAD6</i>-overexpressing plants. Our results indicate that the <i>GhCAD6</i> gene is predominantly expressed during the stages of fiber elongation and secondary wall synthesis. Overexpression of the <i>GhCAD6</i> gene resulted in increased plant lignin content and fiber upper half mean length, boll number per plant, fiber uniformity index, strength, and lint were improved. The fiber surface was smoother, and the fiber cell wall was more compact. These findings demonstrate that the <i>GhCAD6</i> gene positively regulates lignin synthesis and fiber quality formation, contributing to the enhancement of cotton fiber quality.