Fruit sweetness depends on how efficiently sugars are produced, transported, and stored during ripening. Previous studies have shown that hormones such as ethylene and abscisic acid (ABA) play major roles in fruit maturation, and that MYB-family transcription factors can either promote or suppress sugar accumulation in different fruit crops. Grapes, as a classic non-climacteric fruit, offer an especially valuable system for studying how ABA controls ripening. However, although ABA has long been associated with improved color, flavor, and sugar content, the precise transcriptional machinery connecting this hormone to sugar metabolism in grape berries has remained poorly defined. Based on these challenges, in-depth research into the molecular basis of ABA-induced sugar accumulation in grapes is needed.
A research team from Shanghai Jiao Tong University published (DOI: 10.1093/hr/uhaf318) the study on February 18, 2026, in Horticulture Research, showing that ABA promotes grape ripening and sugar accumulation through a molecular complex formed by VvMYB44 and VvERF045, which activates the key sucrose-metabolism gene VvSPS4.
To trace how ABA reshapes grape ripening, the team treated pre-veraison ‘Muscat Hamburg’ berries with ABA and tracked physiological and transcriptional changes across four developmental stages. The treatment led to earlier coloration, larger berries, faster total soluble solids accumulation, and markedly higher glucose and fructose contents. Using RNA sequencing, the researchers generated a transcriptome dataset and applied weighted gene co-expression network analysis to identify candidate regulators linked to soluble sugar buildup. This approach revealed five structural genes and 44 transcription factors responsive to ABA. Among them, VvMYB44 stood out because of its strong expression in mature ABA-treated fruit. Functional tests in grape calli and tomato confirmed that overexpressing VvMYB44 increased soluble sugar content. Mechanistic assays then showed that VvMYB44 directly binds the promoter of the VvSPS4 gene and activates its transcription. The story became even more compelling when the team found that VvERF045 physically interacts with VvMYB44, further amplifying activation of VvSPS4. Overexpression of VvERF045 also elevated sugar levels in tomato fruit, strengthening evidence that this two-factor complex acts as a powerful enhancer of sugar accumulation.
“This work moves beyond the observation that ABA promotes ripening and sweetness,” the researchers suggest in essence, “by identifying a defined transcriptional module that connects hormone signaling with sucrose metabolism.” The discovery of the VvMYB44–VvERF045 partnership provides a clearer picture of how ripening signals are translated into biochemical changes that directly affect fruit quality. Rather than acting through a broad and diffuse response, ABA appears to engage a specific regulatory route centered on VvSPS4, offering a more precise explanation for how sweetness develops in grape berries.
The implications extend well beyond grapes. By identifying a molecular switch that links ABA signaling to sugar accumulation, the study opens new possibilities for breeding and biotechnology aimed at improving fruit flavor without relying only on traditional selection. The VvMYB44–VvERF045–VvSPS4 pathway could become a useful target for enhancing sweetness, optimizing harvest quality, and refining ripening control in grapes and potentially other horticultural crops. In a broader sense, the work also provides a framework for understanding how hormone-responsive transcriptional networks shape economically important traits, helping bridge basic plant biology with future applications in fruit improvement and premium crop production.
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References
DOI
10.1093/hr/uhaf318
Original Source URL
https://doi.org/10.1093/hr/uhaf318
Funding information
This research was funded by the Postdoctoral Fellowship Program of CPSF under Grant Number GZB20240439, the Ningbo Science and Technology Development Special Fund (2024S018), the Fujian Province Science and Technology Plan Project (2024S0051), China Agriculture Research System (CARS-29-zp-7), National Natural Science Foundation of China (32102346), and Key Research and Development Program of Shaanxi Province (2023-ZDLNY-28).
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.