Expression of ClPAP and ClPSY1 in watermelon correlates with chromoplast differentiation, carotenoid accumulation, and flesh color formation

Abstract Chromoplast differentiation during flesh development in different watermelon varieties was observed by optical and transmission electron microscopy. Carotenoid analyses by LC–MS/MS revealed that red-fleshed watermelon mainly accumulated lycopene, which eventually shaped into a crystalloid chromoplast near maturation, while the accumulation of other carotenoids led to the formation of globular chromoplasts. Expressions of three phytoene synthase genes (ClPSY) and seven plastid lipid-associated genes (ClPAP) in different flesh development stages were analyzed. Based on our results, the expression of ClPSY1 was consistent with the accumulation of phytofluene and total carotenoids, while that of ClPAP (Cla014416) was consistent with ClPSY1. CDS and promoter sequence variations of ClPSY1 and Cla014416 may be the main reason for the significant expression levels based on gene and promoter cloning.