Fruit ripening determines both food quality and postharvest losses worldwide, yet the molecular mechanisms controlling this process remain incompletely understood. A new study uncovers how salicylic acid, a natural plant hormone, suppresses ethylene production—the key driver of ripening—in apple fruit. The researchers identified a regulatory pathway in which salicylic acid stabilizes a transcription factor that represses ethylene biosynthesis genes, thereby delaying ripening. By preventing protein degradation through a ubiquitination mechanism, the hormone effectively slows biochemical signals that trigger fruit maturation. These findings reveal a previously unknown molecular strategy by which plants regulate ripening timing and provide new insight into controlling fruit longevity at the post-translational level.
Ethylene is a central hormone controlling ripening in climacteric fruits such as apple, tomato, and banana, coordinating color change, softening, and flavor development. While manipulating ethylene production has long been a target for improving fruit storage, most approaches focus on enzyme activity or gene expression rather than upstream regulatory mechanisms. Salicylic acid has been known to delay ripening in several crops, but how it suppresses ethylene biosynthesis at the molecular level has remained unclear. Increasing postharvest losses and global demand for longer-lasting fresh produce highlight the urgency of understanding hormone interactions controlling ripening. Based on these challenges, it is necessary to conduct in-depth research into the molecular mechanisms linking salicylic acid signaling with ethylene regulation.
Researchers from Shenyang Agricultural University and collaborating institutions reported (DOI: 10.1093/hr/uhaf303) on November 6, 2025, in Horticulture Research that salicylic acid suppresses apple fruit ripening through a previously unknown protein-regulation pathway. The team demonstrated that the hormone controls ethylene biosynthesis by modulating ubiquitination-mediated protein degradation. Their work identified a regulatory module involving the WRKY transcription factor MdWRKY40 and the ubiquitin ligase MdPUB24, revealing how hormone signaling reshapes protein stability to influence ripening. The study provides molecular evidence explaining how salicylic acid delays fruit maturation and extends storage potential.
The researchers first confirmed that salicylic acid treatment significantly reduced ethylene production and delayed visible ripening symptoms such as fruit yellowing during storage. Molecular analyses revealed that salicylic acid increased expression of the WRKY transcription factor MdWRKY40, which acts as a repressor of the ethylene biosynthesis gene MdACS1 , a key rate-limiting regulator controlling ethylene formation.
Further experiments showed that MdWRKY40 directly binds to W-box elements within the promoter of MdACS1 , suppressing its transcription. When MdWRKY40 expression was silenced, ethylene production increased even under salicylic acid treatment, confirming its essential regulatory role.
The study then uncovered a deeper regulatory layer. Scientists identified the U-box E3 ubiquitin ligase MdPUB24, which physically interacts with MdWRKY40 and targets it for degradation through the 26S proteasome pathway. Salicylic acid reduced expression of MdPUB24 , thereby preventing ubiquitination of MdWRKY40 and stabilizing the transcription factor protein. This stabilization strengthened repression of MdACS1 and ultimately lowered ethylene biosynthesis.
Protein interaction assays, ubiquitination experiments, and degradation analyses demonstrated that salicylic acid regulates ripening not only transcriptionally but also post-translationally by controlling protein stability. This MdPUB24–MdWRKY40– MdACS1 regulatory module represents a newly discovered molecular switch governing apple fruit ripening.
According to the researchers, the findings redefine how plant hormones regulate fruit development. Rather than simply altering gene expression, salicylic acid reshapes protein stability through ubiquitination pathways, creating a precise molecular “brake” on ripening. Understanding post-translational regulation helps explain why hormone treatments produce strong physiological effects. By identifying a specific regulatory module linking hormone signaling to ethylene biosynthesis, the study establishes a mechanistic framework that may extend beyond apple to other climacteric fruits and provides new insight into the complex hormonal coordination underlying fruit maturation.
The discovery has important implications for agriculture, food storage, and supply-chain sustainability. By targeting regulators such as MdPUB24 or stabilizing MdWRKY40 protein activity, breeders and postharvest technologies may slow ripening without compromising fruit quality. Such strategies could extend shelf life, reduce transportation losses, and decrease reliance on chemical preservatives. Similar ubiquitination-based regulatory systems may operate in other commercially important fruits, suggesting broad application potential. As global food systems seek solutions to reduce waste while maintaining freshness, molecular insights into hormone-controlled ripening provide a promising foundation for precision postharvest management and next-generation crop improvement strategies.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhaf303
Funding information
This work was supported by the Liaoning Provincial Major Special Project of Science and Technology (2025JH1/11700014) and the National Natural Science Foundation of China (32402532).
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.
Horticulture Research
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Salicylic acid reduces MdPUB24-mediated ubiquitination of MdWRKY40 to suppress ethylene biosynthesis in apple fruit
29-Oct-2025
The authors declare that they have no competing interests.