Development of a “Golden fiber” cotton germplasm via carotenoid biofortification

Natural colored cotton (NCC) offers a sustainable, dye-free, and eco-friendly alternative for producing colored textiles. Carotenoids, a group of important natural liposoluble pigments, are known for their diverse color spectrum. In this study, we successfully engineered the carotenoid biosynthesis pathway specifically in cotton fibers by utilizing a fiber-specific GbEXPA2 promoter and a CaMV 35S promoter to drive the expression of two key carotenoid biosynthesis genes, CrtB and CrtI, respectively. This approach resulted in the development of a golden fiber cotton germplasm enriched with β-carotene. Notably, the pigmentation was predominantly observed during the early developmental stages of the fiber (5–20 d post-anthesis). While the presence of carotenoids had no significant effect on plant architecture and growth, it positively influenced the fiber elongation rate, albeit with a slight reduction in fiber length and strength. This study represents a pioneering strategy for the future development of NCCs through carotenoid biofortification.