The gibberellin-activated transcription factor MdRAV1 regulates ethylene biosynthesis to suppress apple fruit ripening

The phytohormone ethylene is vital for the ripening of climacteric fruit, such as apples (Malus domestica). The gibberellin (GA) class of phytohormones affects ethylene biosynthesis during ripening via an unknown molecular mechanism. Here, we investigated the effects of GAs on apple fruit ripening. We observed that endogenous GA accumulation was opposite to that of ethylene production during apple fruit development. Moreover, exogenous GA treatment suppressed ethylene production and fruit ripening. However, treatment with a GA biosynthesis inhibitor promoted ethylene production and accelerated fruit ripening in apple, suggesting that GA suppresses ripening. GA treatment enhanced the expression of the transcription factor Related to ABSCISIC ACID INSENSITIVE3/VIVIPAROUS1 (MdRAV1) during apple ripening. The DELLA protein GA INSENSITIVE (MdGAI) interacted with MdRAV1 and suppressed its DNA-binding and regulatory activities. GA triggered MdGAI removal, thereby releasing MdRAV1. GA-activated MdRAV1 bound to the promoter of MdACS1, encoding 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, and directly suppressed its transcription. These results suggest that GA-activated MdRAV1 suppresses MdACS1 transcription, reducing ethylene production and suppressing fruit ripening.