Breeding triple-advantage cottonseed with higher yield, enhanced nutrition, and reduced toxicity by redirecting terpenoid metabolism to astaxanthin

Cottonseed is a valuable source of edible oil and protein, but its utilization is limited by high gossypol content. In this study, we engineered cotton (Gossypium hirsutum) to biosynthesize astaxanthin through both single-gene (CrBKT) and multi-gene (CrBKT, ZmPSY1, PaCrtI, HpCrtZ) expression strategies. Transgenic cotton plants exhibited significant astaxanthin accumulation across multiple tissues, with distinct red pigmentation observed in leaves, stems, reproductive organs, and cottonseeds. While single CrBKT expression was sufficient to redirect metabolic flux toward astaxanthin biosynthesis, multi-gene transformation did not necessarily lead to higher astaxanthin levels, suggesting that BKT is the key determinant of astaxanthin accumulation in cotton. Additionally, BKT-overexpressing plants produced larger cottonseeds, with increased seed weight and size, indicating a possible link between carotenoid metabolism and seed development. Importantly, gossypol content was significantly reduced in transgenic cottonseeds, likely due to the redistribution of terpene metabolism. The qRT-PCR analyses confirmed that the expression of key gossypol biosynthetic genes was downregulated, supporting a metabolic trade-off between astaxanthin and gossypol biosynthesis. These results demonstrate that cotton can serve as a biofactory for astaxanthin production, providing a scalable and cost-effective alternative to traditional sources. Furthermore, the dual benefits of enhanced nutrition and reduced toxicity significantly expand the potential applications of cottonseed in human food, animal feed, and functional ingredient markets.