How grape siblings split aroma destiny: A master switch that turns fragrance on and off
image: A model for the molecular basis underlying differential monoterpenoid glycosylation and 'Muscat' flavor intensity in RDHY and RDXY berries.
Credit: Horticulture Research
Grape aroma is shaped not only by the volatile compounds we can smell but also by their non‑volatile, sugar‑bound counterparts—flavour precursors locked away until fermentation releases them. Now, researchers have uncovered the genetic machinery that controls this hidden aroma reservoir in grapes. By comparing two sibling grape varieties with strikingly different scent profiles, the team identified a small set of glycosyltransferase enzymes and a master transcription factor that together drive the conversion of free fragrant compounds into stored, sugar‑linked forms. The findings open new avenues for precisely engineering grape and wine aroma through targeted breeding or biotechnology.
Monoterpenoids—compounds like linalool, geraniol, and citronellol—are the backbone of the floral, citrusy “Muscat” character that defines many of the world’s most prized grape varieties and wines. In grape berries, these molecules exist in two forms: free volatiles that deliver immediate scent, and glycosidically‑bound precursors that are non‑volatile but can be unlocked during winemaking to enhance aroma complexity. The balance between these two pools determines not just how a grape smells fresh off the vine, but the aromatic potential of the wine it becomes. Despite the importance of this glycosylation step, the genes that control it—and how they are regulated—have remained largely unidentified. Based on these challenges, there is a need for in‑depth research into the molecular regulators that govern glycosylated monoterpenoid accumulation in grapes.
A team led by researchers at China Agricultural University and Beijing Forestry University has uncovered the genetic drivers behind glycosylated monoterpenoid accumulation in grapes. Their findings, published (DOI: 10.1093/hr/uhag188) May 8, 2026, in Horticulture Research, reveal how a transcription factor called VviMYB174 activates a suite of glycosyltransferase (GT) enzymes—VviGT22, VviGT37, and VviGT74—to lock fragrant monoterpenoids into sugar‑bound precursors. The study also explains why two sibling grape varieties, ‘Ruiduhongyu’ and ‘Ruiduxiangyu’, diverge so dramatically in their aroma profiles.
The researchers compared ‘Ruiduhongyu’ (RDHY), a pink‑skinned grape with subdued Muscat character, and its green‑skinned sibling ‘Ruiduxiangyu’ (RDXY), which carries an intense Muscat perfume. Across seven developmental stages, RDHY accumulated up to 1.8‑fold more glycosylated monoterpenoids and 2.0‑fold fewer free volatiles than RDXY. Transcriptome analysis ruled out differences in the core terpenoid biosynthesis pathway—instead, the divergence traced to five glycosyltransferase genes whose expression soared during late ripening in RDHY.
Among these, three previously uncharacterized enzymes—VviGT22, VviGT37, and VviGT74—were confirmed through in vivo and in vitro assays to possess robust monoterpenol glycosylation activity. The transcription factor VviMYB174 emerged as the master regulator: it binds directly to the promoters of these three GT genes and drives their expression. Intriguingly, the promoter of VviMYB174 differed significantly between the two varieties—RDXY’s version lost the binding site for VviMYB174, effectively silencing the gene. This natural promoter variation, combined with lower VviMYB174 expression in RDXY, explains why one sibling locks away its fragrance while the other lets it fly free. The study also found that a single amino acid change (L186V) inactivates VviGT7 in RDHY, disqualifying it as a contributor to the phenotype.
“We were surprised to find that the difference in aroma between these two sibling grapes comes down to a small set of enzymes and one transcription factor—not the entire biosynthetic pathway,” the authors said. “What's particularly exciting is that a natural mutation in the promoter of VviMYB174 essentially disables the glycosylation machinery in one variety, while the other keeps it running at full capacity. This gives us a very clear genetic handle for manipulating grape aroma, whether through breeding or biotech approaches.”
These findings offer winemakers and grape breeders a precise toolkit for tailoring aroma profiles. By modulating the expression of VviMYB174 or its downstream GT targets, it may become possible to fine‑tune the balance between immediate fragrance and fermentation‑released aroma potential—allowing varieties to be optimized for fresh consumption, sparkling wines, or age‑worthy reds. The discovery also highlights the power of natural promoter variation as a source of trait diversity, pointing to new strategies for marker‑assisted breeding. For the wine industry, where aroma is a primary driver of quality and value, this work provides a molecular roadmap for crafting grapes with precisely calibrated scent profiles—from boldly perfumed table grapes to elegantly structured wines with hidden complexity waiting to be unlocked.
###
References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhag188
Funding information
Key R&D projects in Ningxia Hui Autonomous Region (2024BBF01002) and National Natural Science Foundation of China (32072513).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.