Salicylic acid (SA) is a central hormone involved in plant immunity and the initiation of defense-related gene expression. Plants can fine-tune immune responses by converting SA into inactive or storage forms through enzymatic modification. Although Arabidopsis and other model plants have been used to characterize SA-related enzymes, little is known about how these mechanisms operate in major fleshy fruits, which are especially susceptible to postharvest pathogens. These crops often experience aggressive decay during transport and storage, resulting in large economic losses. Due to these challenges, there is a pressing need to understand how SA-modifying enzymes regulate immune responsiveness in fruit and how this knowledge can be used to improve disease resistance.
In a study published (DOI: 10.1093/hr/uhaf049) in Horticulture Research on 1 June 2025, researchers identified the peach UDP-glycosyltransferase PpUGT74F2 as a major enzyme involved in SA metabolism. Through biochemical assays, gene expression profiling, and functional tests in both peach and transgenic tomato, the study demonstrates that PpUGT74F2 converts SA to salicylic acid glucoside (SAG) and acts as a negative regulator of fruit immunity. The findings clarify how SA storage pathways influence disease susceptibility and highlight an immune control mechanism that had not been previously described in fruit crops.
The research team first analyzed members of the UDP-glycosyltransferase gene family in peach fruit and identified PpUGT74F2 as the most highly expressed candidate associated with SA metabolism. Enzymatic assays confirmed that PpUGT74F2 catalyzes the conversion of SA into its glucoside SAG, reducing the pool of active SA available for immune signaling. When peach fruit were infected with the brown rot pathogen Monilinia fructicola, PpUGT74F2 expression decreased, while SA, methyl salicylate (MeSA), and defense-related gene expression increased, suggesting that suppression of the enzyme supports immune activation.
To test the functional consequences, PpUGT74F2 was overexpressed in tomato. Transgenic tomato fruit accumulated significantly higher SAG levels but did not increase MeSAG, demonstrating selective glycosylation of SA in vivo. Importantly, these tomatoes displayed heightened susceptibility to Botrytis cinerea and Pseudomonas syringae, with reduced MeSA accumulation and lower expression of pathogenesis-related genes. This shows that PpUGT74F2 weakens immunity by diverting SA away from the MeSA-mediated defense signaling pathway.
“Our findings reveal that PpUGT74F2 serves as a molecular brake on immune signaling in fruit,” the authors noted. “By directing SA into a stored, inactive form, the enzyme reduces the production of MeSA, a key mobile defense signal. This mechanism explains why fruits sometimes fail to mount strong resistance to pathogens. It also highlights potential intervention points for improving disease resistance without altering fruit development.”
This work demonstrates that modifying SA glycosylation can substantially influence disease resistance in fruit crops. Targeting PpUGT74F2 or related enzymes could help breeders and biotechnologists enhance natural immunity in peach, tomato, and other commercially important fruits. Such strategies may reduce postharvest spoilage, limit reliance on fungicides, and support sustainable fruit supply chains under increasing climate and pathogen pressures. Future research may focus on selectively modulating SA-to-MeSA conversion to strengthen immune signaling while maintaining fruit quality and flavor.
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References
DOI
10.1093/hr/uhaf049
Original Source URL
https://doi.org/10.1093/hr/uhaf049
Funding information
This work was supported by Zhejiang Provincial Natural Science Foundation (LD22C150001) and Ningbo Key Research and Development Program (2022Z179).
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.