A VvMADS module links carotenoid metabolism with ABA biosynthesis to promote norisoprenoid accumulation in grape berry

Abstract

Norisoprenoids are key aroma compounds in wine grapes (Vitis vinifera L.), derived from carotenoid cleavage, yet the transcriptional mechanisms coordinating their biosynthesis remain poorly understood. Here, we identified two MADS-box transcription factors from distinct subfamilies, VvMADS4 (VvSEP3) and VvTM6 (VvAP3.2), whose expression strongly correlates with norisoprenoid accumulation during grape berry ripening. Transient overexpression in berries and stable transformation of calli showed that both transcription factors independently promoted norisoprenoid production, while their co-expression led to synergistic enhancement. Transcriptomic and metabolic analyses showed that VvMADS4 and VvTM6 were associated with increased expression of genes involved in carotenoid, norisoprenoid, and abscisic acid (ABA) biosynthesis, including phytoene synthase 1 (VvPSY1), neoxanthin-deficient 1 (VvNXD1), and 9-cis-epoxycarotenoid dioxygenases (VvNCEDs). Mechanistically, VvTM6 directly binds to and activates the VvNXD1 promoter, thereby promoting neoxanthin synthesis and redirecting carotenoid metabolic flux toward neoxanthin and norisoprenoid production. In contrast, VvMADS4 enhances norisoprenoid biosynthesis through physical interaction with VvTM6, without directly binding to the VvNXD1 promoter. Furthermore, VvMADS2 directly activates VvNCED1, leading to increased ABA and norisoprenoids, while also interacting with VvMADS4 and VvTM6. Collectively, these findings reveal a MADS module that integrates carotenoid metabolism with ABA biosynthesis to promote norisoprenoid accumulation during grape berry ripening, providing potential targets for improving grape aroma quality.