Temperature Dominates Light in Regulating Lycopene During a Critical Period in Postharvest Tomato Fruit

Fruit coloration is a key determinant of tomato quality, yet how light and temperature interact to regulate pigmentation during ripening remains unclear. Using a semi-in-fruit experimental system, we demonstrate that while high light accelerates chlorophyll degradation and lycopene accumulation at 25 °C, supra-optimal temperature (40 °C) completely abolishes lycopene biosynthesis irrespective of light conditions, primarily through transcriptional suppression of SlPSY1 and SlGGPS2. Elevated postharvest temperatures (≥30 °C) not only change the carotenoid composition but also reduce the antioxidant capacity and vitamin C content in fruit. Temperature-switch experiments revealed a critical developmental window, days 2–4 after ethylene treatment, during which temperature exerts dominant control over carotenoid metabolism. Exposure to high temperature within this window irreversibly shifts pigment accumulation from lycopene to yellow/orange carotenoids. These findings identify a temporally precise regulatory nexus integrating environmental signals with the ripening program, offering a framework for targeted temperature management to optimize tomato color and nutritional quality.