Phytoene synthase (PSY) is the primary rate-limiting enzyme in the carotenoid biosynthesis pathway and plays a crucial role in regulating carbon flux toward carotenoid production. The Orange (OR) protein functions as a molecular chaperone for PSY, increasing its activity and facilitating carotenoid accumulation. Notably, the mutation of OR to OR His further amplifies this effect. However, the interaction dynamics between OR/OR His and multiple PSY copies in plants remain unclear, particularly whether these proteins interact uniformly with all PSY variants or exhibit differential effects. We here cloned three BoaPSY homologs from Chinese kale and demonstrated that all identified BoaPSYs contribute to carotenoid accumulation in engineered bacterial systems and Chinese kale calli. Among them, BoaPSY1 exerted the most pronounced effect, followed by BoaPSY2 and BoaPSY3. Additionally, BoaOR/OR His directly interacted with BoaPSYs, and the overexpression of BoaOR/OR His – BoaPSYs complexes further enhanced carotenoid accumulation in Chinese kale calli, with the calli overexpressing BoaOR His - BoaPSY1/2 showing the highest carotenoid content. Binding energy analyses and α-galactosidase activity assays revealed that BoaOR His has the strongest binding affinity for BoaPSY2. Overexpression of the BoaOR His – BoaPSY2 complex in Chinese kale plants increased carotenoid and chlorophyll levels but reduced their degradation during postharvest storage. Our findings advance the understanding of carotenoid metabolic regulation and propose a novel strategy for improving both preharvest quality and postharvest shelf life of Chinese kale, thereby increasing its economic value and market potential.
Zhang et al. (Fri,) studied this question.