Tea plant enzyme weakens immunity by lowering salicylic acid levels
image: Mechanism model of CsUGT74B5 function in fine-tuning the SA levels and coordinated plant resistance to anthracnose. Image link: https://academic.oup.com/view-large/figure/508296909/uhaf009f10.tif
Credit: Horticulture Research
Tea plants (Camellia sinensis) face frequent attacks from pathogens such as Colletotrichum camelliae, which causes anthracnose and severely reduces leaf quality and yield. Plant hormones like salicylic acid play vital roles in orchestrating immune responses, yet maintaining appropriate levels of free salicylic acid (SA) is essential—too little compromises resistance, while too much causes metabolic stress. Enzymatic modifications such as hydroxylation and glycosylation are known to regulate SA activity in several species, but their precise roles in tea plants have remained unclear. Due to these challenges, it is necessary to conduct in-depth research on how SA derivatives regulate tea plant disease resistance.
Researchers from Qingdao Agricultural University and Anhui Agricultural University have uncovered the function of a glycosyltransferase gene, CsUGT74B5, which regulates SA metabolism in tea plants. The findings were published (DOI: 10.1093/hr/uhaf009) on April 1, 2025, in Horticulture Research by Oxford University Press. The study reveals that CsUGT74B5 specifically catalyzes the glucosylation of SA and 2,6-dihydroxybenzoic acid, converting them into inactive glucosides. This biochemical process suppresses disease resistance and enhances anthracnose susceptibility, highlighting a delicate molecular balance between plant defense activation and hormone homeostasis.
Using gene expression profiling, the team found that CsUGT74B5 expression was sharply downregulated when tea plants were infected with C. camelliae. Laboratory assays confirmed that the recombinant CsUGT74B5 enzyme catalyzed the glucosylation of SA and 2,6-dihydroxybenzoic acid (2,6-DHBA) specifically at their ortho-hydroxyl groups, with no activity toward other derivatives. Structural modeling and molecular docking supported this substrate selectivity, showing tight binding with SA and 2,6-DHBA in the enzyme’s active pocket. When CsUGT74B5 was overexpressed in Arabidopsis thaliana, tobacco, and tea leaves, the plants accumulated higher levels of the inactive conjugate SAG but lower levels of free SA—corresponding with accelerated lesion formation and weaker resistance to anthracnose. Conversely, external application of SA inhibited fungal growth and significantly reduced lesion spread. The study’s findings identify CsUGT74B5 as a negative regulator of disease resistance that fine-tunes SA homeostasis and reveals a new glucosylation pathway involved in plant immune modulation.
"Our research reveals that CsUGT74B5 acts as a ‘molecular switch’ in the SA network," said Prof. Lei Zhao, the study’s corresponding author. "By converting active SA into its glucoside form, this enzyme weakens the plant's immune response and makes it more vulnerable to infection. This discovery not only deepens our understanding of hormone regulation in tea plants but also provides a potential target for improving disease resistance through gene editing or breeding strategies."
The identification of CsUGT74B5 opens new possibilities for developing disease-resistant tea cultivars. By manipulating the gene’s expression or activity, breeders could enhance SA accumulation, thereby strengthening natural defense systems against anthracnose and other fungal pathogens. Beyond tea, the findings contribute to broader plant science by elucidating how glucosylation regulates hormone homeostasis and immunity in crops. This research also provides biochemical insights valuable for synthetic biology applications, such as engineering tailored glycosyltransferases to optimize stress responses and secondary metabolite production in economically important plants.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhaf009
Funding information
This work was supported by the Youth Innovation and Science Technology Support Program (2021KJ103), Natural Science Foundation of China (32272775, 32372764), Natural Science Foundation of Shandong province (ZR2022MC088), and Technology System of Modern Agricultural Industry in Shandong Province (SDAIT-19-00).
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, 2024. 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.