Ubiquitin switch reveals how grapevines survive the cold

Cold temperatures can severely damage perennial crops such as grapevine, limiting growth, fruit quality, and regional distribution. Plants respond to cold through complex signaling networks that coordinate transcriptional activation, protein turnover, and oxidative stress detoxification. Central among these systems is the ubiquitin–proteasome pathway, which selectively removes regulatory proteins to fine-tune stress responses. Transcription factors like MYB proteins and CBF regulators are essential for activating COR genes, but their stability is tightly controlled by E3 ubiquitin ligases. Yet, in grapevine, the mechanisms linking ubiquitination to cold-response transcriptional programs and ROS homeostasis remain unclear. Due to these challenges, deeper investigation into grapevine cold-tolerance mechanisms is urgently needed.

A research team from Ningxia University reported a new regulatory mechanism underlying grapevine cold tolerance in a study published (DOI: 10.1093/hr/uhaf093) on March 22, 2025 in  Horticulture Research. The researchers identified VaMIEL1, a RING-type E3 ubiquitin ligase, as a key negative regulator that promotes degradation of the transcription factor VaMYB4a under normal temperatures. Cold stress suppresses VaMIEL1 expression, allowing VaMYB4a to activate the CBF–COR pathway and antioxidant defenses. The study combines biochemical analysis, Arabidopsis genetics, and grapevine callus experiments to map this cold-response module.

The researchers first demonstrated that VaMIEL1 physically interacts with VaMYB4a through yeast two-hybrid, BiFC, and co-immunoprecipitation assays, with the C-terminal regulatory domain of VaMYB4a responsible for binding. Promoter analysis revealed a low-temperature-responsive element, and reporter assays confirmed that VaMIEL1 expression decreases dynamically during cold exposure. In Arabidopsis, overexpression of VaMIEL1 increased cold sensitivity, leading to elevated ROS accumulation, reduced proline levels, impaired antioxidant enzyme activity, and strong suppression of CBF and COR gene expression. Conversely, the AtMIEL1 loss-of-function mutant showed improved cold tolerance and enhanced redox balance.

In grapevine calli, VaMIEL1 overexpression caused browning, reduced biomass, high ROS buildup, and lower SOD/POD activity under cold conditions. RNAi silencing of VaMIEL1 produced the opposite effects, elevating antioxidant capacity and restoring expression of VaCBF1 and VaCBF3. In vitro and in vivo ubiquitination assays confirmed that VaMIEL1 directly ubiquitinates VaMYB4a, accelerating its proteasomal degradation. Co-expression experiments further demonstrated that VaMIEL1 partially suppresses VaMYB4a-mediated cold tolerance, highlighting their opposing roles in modulating the CBF–COR pathway. Together, these results reveal an integrated mechanism linking ubiquitination, transcriptional activation, and oxidative stress mitigation during cold adaptation.

“Our findings demonstrate that cold tolerance in grapevine is not governed by a single pathway but instead by a coordinated system integrating transcriptional control and redox balance,” said the study’s corresponding author. “By identifying VaMIEL1 as a key regulator that destabilizes VaMYB4a, we show how the plant fine-tunes CBF–COR signaling and antioxidant activity in response to cold. This dual regulatory role expands our understanding of how perennial species survive harsh environments and provides a promising molecular handle for future crop improvement.”

The newly uncovered VaMIEL1–VaMYB4a module provides a valuable framework for breeding and engineering cold-resistant grapevine cultivars. Targeted suppression of VaMIEL1 or enhancement of VaMYB4a stability could improve CBF–COR activation and ROS detoxification, supporting plant survival during early-season frosts or extreme climate events. Because many crops rely on similar MYB- and ubiquitination-based regulatory networks, the findings may extend beyond grapevine, offering potential applications in apples, pears, and other temperate fruit species. This work opens new avenues for developing climate-adaptive crops that can sustain yield and quality under increasing environmental variability.

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References

DOI

10.1093/hr/uhaf093

Original Source URl

https://doi.org/10.1093/hr/uhaf093

Funding information

The gift of the Arabidopsis mutant miel1 (SALK_087883) from Zheng Yuan’s team at the State Key Laboratory of Crop Adaptation and Improvement, School of Life Sciences, Henan University, is greatly appreciated. This work is supported by Ningxia Hui Autonomous Region Key R&D Program (Grant no. 2023BCF01003), National Natural Science Foundation of China (Grant no. 32472711 and 32060672), and Agricultural Breeding Project of Ningxia Hui Autonomous Region (Grant no. NXNYYZ202101).

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.