New Regulatory Pathway Enhances Key Aroma Compound in Wine Grapes

β-Damascenone is a key norisoprenoid compound responsible for characteristic floral and fruity aromas in grapes and wines, particularly those from non-aromatic varieties such as Cabernet Sauvignon and Merlot. Its biosynthesis originates from carotenoid precursors and is influenced by developmental cues and environmental conditions. Previous studies have shown that abscisic acid (ABA) can increase β-damascenone levels during berry ripening, yet the regulatory network linking ABA signaling to norisoprenoid production has remained unresolved. Understanding how grape berries coordinate hormonal regulation and volatile formation is important for improving wine sensory quality. Due to these challenges, there is a need to investigate the molecular regulators driving β-damascenone biosynthesis.

Researchers from the Center for Viticulture and Enology at China Agricultural University have discovered a regulatory mechanism that enhances β-damascenone formation in grape berries. The study, published (DOI: 10.1093/hr/uhaf017) on May 1, 2025, in Horticulture Research, reveals that the transcription factor VviWRKY24 directly activates the ABA biosynthetic gene VviNCED1. This increase in ABA subsequently induces expression of VviCCD4b, leading to elevated β-damascenone accumulation.

Through gene overexpression, gene silencing, RNA-sequencing, promoter binding assays, and metabolite profiling, the study demonstrated that VviWRKY24 functions as a positive regulator of β-damascenone biosynthesis in grapes. When VviWRKY24 was overexpressed in grape leaves, berries, and calli, β-damascenone levels significantly increased, particularly in berry tissues where this compound is naturally most abundant. Conversely, silencing VviWRKY24 reduced norisoprenoid content.

Mechanistically, VviWRKY24 was shown to directly bind to the promoter of VviNCED1, a key gene in ABA biosynthesis, and activate its transcription. Elevated ABA levels were then found to induce VviCCD4b, which catalyzes a key carotenoid cleavage step linked to β-damascenone formation. Electrophoretic mobility shift assays confirmed the binding of VviWRKY24 to the VviNCED1 promoter, and dual-luciferase assays supported its role as a transcriptional activator.

Importantly, the effects of VviWRKY24 did not stem from increasing total carotenoid concentrations, indicating that the transcription factor regulates the metabolic flux toward β-damascenone rather than precursor abundance. This establishes VviWRKY24 as an upstream molecular switch coordinating hormonal signaling and aroma formation during berry ripening.

"Our findings reveal a clear regulatory link between ABA signaling and aroma compound biosynthesis in grape berries," said the study's corresponding author. "By identifying VviWRKY24 as a key activator of VviNCED1 and β-damascenone formation, we provide a strategic molecular target for enhancing grape and wine aroma quality. This discovery also expands our understanding of hormone-regulated secondary metabolism in fruit development."

This research provides valuable insights for grape and wine production. By modulating VviWRKY24 or ABA-related pathways, breeders and viticulturists may enhance desirable aroma attributes without altering grape variety or fermentation processes. The identified regulatory mechanism could also inform targeted breeding, gene editing, biostimulant treatments, or vineyard management strategies that promote high-quality flavor profiles under diverse growing conditions. Additionally, the results highlight the broader significance of hormonal regulation in fruit aroma development, offering potential applications in other fruit crops where volatile compounds shape sensory value.