Grapes are one of the world’s most valuable fruit crops, but growers often struggle with low fruit set due to high rates of young berry drop—especially in popular cultivars like ‘Kyoho’. To address this, the synthetic cytokinin CPPU has become a common solution for enhancing fruit retention. Despite its widespread use, the internal molecular mechanics behind CPPU’s effects remain unclear. Researchers have long suspected that cytokinin-related genes and transcription factors play central roles in fruit set, but direct evidence in grapevine is scarce. Due to these challenges, there is a growing need to dissect how CPPU orchestrates genetic responses to drive successful fruit initiation.
A research team from the College of Horticulture and Plant Protection at Henan University of Science and Technology has shed new light on the genetic machinery behind fruit set in grapevines. Their study (DOI: 10.1093/hr/uhae183), published on July 10, 2024, in Horticulture Research, reveals that the transcription factor VlMYB59 activates VlCKX4, a gene involved in cytokinin metabolism, to promote CPPU-induced fruit set. By combining transcriptomic profiling, hormonal assays, and gene overexpression in Arabidopsis, the team mapped a regulatory cascade that could help breeders and growers improve fruit yields through targeted interventions.
Using five developmental stages of grape berries treated with CPPU and water, the researchers generated high-resolution transcriptome profiles and proposed a novel screening method called value differentially expressed genes (VDEGs). Among the VDEGs, VlCKX4 emerged as a key cytokinin metabolism gene significantly upregulated after CPPU treatment. Functional experiments in Arabidopsis confirmed that overexpressing VlCKX4 increased fruit number, weight, and plant height, supporting its role in fruit development.
Network analysis then spotlighted VlMYB59 as an upstream regulator. The team demonstrated that VlMYB59 binds directly to the promoter of VlCKX4 and activates its expression. Reporter gene assays, GUS staining, and yeast one-hybrid experiments confirmed this interaction. Notably, overexpressing VlMYB59 also led to enhanced fruit set, indicating both genes contribute independently and synergistically. Hormonal measurements revealed that CPPU modulates auxin, gibberellin, and cytokinin levels—providing the physiological context for this genetic regulation. Together, the data paint a clear picture: VlMYB59 responds to CPPU, switches on VlCKX4, and fine-tunes hormone balance to favor fruit retention and growth.
“Our findings uncover a clean and testable pathway by which CPPU promotes fruit set in grapevines,” said Professor Yihe Yu, corresponding author of the study. “The VlMYB59-VlCKX4 module offers a molecular explanation for how hormone signals are translated into developmental outcomes. It not only advances our understanding of fruit biology but also provides genetic tools that could be harnessed to boost productivity in viticulture and other fruit crops. This is a step toward more precise, gene-guided agricultural practices.”
The discovery of the VlMYB59-VlCKX4 regulatory module opens promising avenues for crop improvement. Breeders can explore these genes as markers for selecting high fruit-set traits, while agronomists may refine CPPU application strategies to align with the gene activation timeline. The innovative VDEG approach introduced in this study also offers a powerful method to identify key regulatory players in other crops. In the long term, gene editing or transgenic techniques targeting this module could help develop grapevine cultivars with consistently higher yields, less hormone input, and improved resilience in variable environments—advancing both scientific understanding and agricultural sustainability.
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References
DOI
10.1093/hr/uhae183
Original Source URL
https://doi.org/10.1093/hr/uhae183
Funding information
This work was supported by National Natural Science Foundation of China (Grant No. 32072517), Program for Science & Technology Innovation Talents in Universities of Henan Province (Grant No. 21HASTIT035), Top Young Talents in Central Plains (Grant No. Yuzutong (2021)44), and PhD Research Startup Foundation of Henan University of Science and Technology (Grant No. 13480077).
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.