Role of VvNCED1 in β-damascenone and abscisic acid biosynthesis: new insights into aroma development in grapes

Abstract

β-Damascenone is a key norisoprenoid in grape (Vitis vinifera L.) that imparts floral and fruity aromas to both fruits and wines. It is derived from carotenoid metabolism, with neoxanthin as a substrate. While its biosynthesis and regulation are not fully understood, abscisic acid (ABA), another metabolite of this pathway, plays a vital role in fruit ripening and stress responses, including drought and cold tolerance. This study investigates the role of grapevine 9-cis-epoxycarotenoid dioxygenase 1 (VvNCED1) in the biosynthesis of ABA and β-damascenone, and its involvement in stress responses.

We analyzed the transcriptome and aroma metabolome of Cabernet Sauvignon grapes across developmental stages. The results show that aroma metabolism is stage-dependent, with norisoprenoid accumulation beginning as grapes start to veraison. VvNCED1 expression positively correlated with β-damascenone levels. Overexpression of VvNCED1 promoted ABA accumulation, while exogenous ABA treatment upregulated genes involved in neoxanthin synthesis (VvNXS, Neoxanthin synthase) and cleavage (VvNCED1), leading to increased β-damascenone levels. These findings suggest that ABA mediates the promotion of β-damascenone through VvNCED1. Additionally, drought stress induced by PEG6000 increased ABA levels in grapevine adventitious roots, supporting the role of ABA in stress responses.

Moreover, we propose another mechanism by which VvNCED1 facilitates β-damascenone biosynthesis: VvNCED1 cleaves 9’-cis-neoxanthin into C25-allenic-apo-aldehydes, which are further cleaved by carotenoid cleavage dioxygenase 1 (VvCCD1) into grasshopper ketones, a precursor to β-damascenone. This was partially confirmed by in vitro protein expression experiments.

Based on these results, we propose a cooperative model for VvNCED1 and VvCCD1 in β-damascenone biosynthesis, where VvNCED1 generates precursors for both ABA and β-damascenone. These findings provide new insights into the relationship between aroma compound accumulation, berry ripening, and stress responses, with implications for improving grape aroma through deficit irrigation techniques.