VviWRKY24 promotes β-damascenone biosynthesis by targeting VviNCED1 to increase abscisic acid in grape berries

Norisoprenoids, which are produced by the cleavage of various carotenoids, are a class of volatile aroma compounds that widely distributed in plants. In wine, they represent a significant source of floral and fruity aromas. β-Damascenone is the most abundant and important norisoprenoid constituent in grape berries (Vitis vinifera L.) and wines. However, the regulatory mechanism of β-damascenone biosynthesis remains poorly understood. The present study has identified a WRKY transcription factor, VviWRKY24, as a key regulator of β-damascenone accumulation in grape berries. The results of overexpression and gene silencing assays in grape leaves, berries and calli demonstrated that VviWRKY24 altered the flow of norisoprenoid metabolism and influenced the composition ratio of norisoprenoids, particularly enhancing the levels of β-damascenone. The results of the RNA-seq, yeast one-hybrid, electrophoretic mobility shift and dual-luciferase assays provided confirmation that VviWRKY24 promoted abscisic acid (ABA) biosynthesis by directly upregulating the expression of VviNCED1. The increase in ABA content resulted in further induction of the expression of CAROTENOID CLEAVAGE DIOXYGENASE 4B (VviCCD4b) on β-damascenone metabolic pathway. These findings elucidate the upstream regulation of ABA and the promotion of ABA on the accumulation of β-damascenone in grapes. This study contributes to a novel understanding of the regulatory mechanisms of β-damascenone biosynthesis and provides a strategy for improving the aroma quality of grapes and wine.