A STAY‐GREEN protein SlSGR1 regulates lycopene and β‐carotene accumulation by interacting directly with SlPSY1 during ripening processes in tomato

Summary As a primary source of lycopene in the human diet, fleshy fruits synthesize this compound both de novo and via chlorophyll metabolism during ripening. Sl SGR 1 encodes a STAY‐GREEN protein that plays a critical role in the regulation of chlorophyll degradation in tomato leaves and fruits. We report that S l SGR 1 can regulate tomato ( S olanum lycopersicum ) lycopene accumulation through direct interaction with a key carotenoid synthetic enzyme S l PSY 1, and can inhibit its activity. This interaction with S l SGR 1 mediates lycopene accumulation during tomato fruit maturation. We confirmed this inhibitory activity in bacteria engineered to produce lycopene, where the introduction of S l SGR 1 reduced dramatically lycopene biosynthesis. The repression of S l SGR 1 in transgenic tomato fruits resulted in altered accumulation patterns of phytoene and lycopene, whilst simultaneously elevating S l PSY 1 m RNA accumulation and plastid conversion at the early stages of fruit ripening, resulting in increased lycopene and β‐carotene (four‐ and nine‐fold, respectively) in red ripe fruits. S l SGR 1 influences ethylene signal transduction via the altered expression of ethylene receptor genes and ethylene‐induced genes. Fruit shelf‐life is extended significantly in S l SGR 1 ‐repressed tomatoes. Our results indicate that S l SGR 1 plays a pivotal regulatory role in color formation and fruit ripening regulation in tomato, and further suggest that S l SGR 1 activity is mediated through direct interaction with PSY 1.