SlATL2 suppresses tomato immunity by degrading SlCSN5a
image: Enhanced Pst DC3000 resistance of SlATL2/SlCSN5a-silenced tomato plants. (A) Representative symptoms and (B) bacterial populations in leaves 3 dpi with Pst DC3000 in VIGS plants targeting the indicated genes. (C) Expression profiling of immune-related genes. Leaves were harvested at 24 hpi, and gene expression was analyzed by qPCR using SlActin as the reference gene. (D) Salicylic acid (SA) contents. (E-F) Accumulation of H2O2. Bars = 5 mm. DAB staining intensity, as determined with ImageJ software. Data were shown as means ± SD; n = 3 (B, C, D, F). Statistically significant differences are indicated by asterisks (*P < 0.05, **P < 0.01, and ***P < 0.001, Student’s t-test) (C). Statistically significant differences are denoted by different letters, as determined by two-way ANOVA followed by Tukey’s test (P < 0.05) (B, D, F). (F) Proposed working model of SlATL2 function in tomato immunity. Upon infection with Pst DC3000, in WT plants, SlATL2 induces the degradation of SlCSN5a, suppressing the SA signaling pathway and ROS production, leading to susceptibility to Pst DC3000. In contrast, the slatl2 mutant accumulates SlCSN5a, which activates the SA pathway and increases ROS, conferring resistance to the pathogen.
Credit: Horticulture Research
The study uncovers the role of SlATL2, an E3 ubiquitin ligase, in regulating tomato immunity against the bacterial pathogen Pseudomonas syringae (Pst) DC3000. The research reveals that SlATL2 negatively regulates immune responses by targeting the COP9 signalosome subunit SlCSN5a for degradation. This process diminishes defense responses, including reactive oxygen species (ROS) production and callose accumulation, crucial for pathogen resistance. The findings highlight a new layer of immune regulation in tomatoes and open up avenues for enhancing crop resistance against bacterial infections through post-translational modification of key immune regulators.
Plants utilize a sophisticated immune system to defend against pathogens, involving both pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). Ubiquitination plays a pivotal role in regulating immune responses, with E3 ubiquitin ligases acting as key mediators. SlATL2, an ATL-type E3 ligase, is implicated in modulating these processes, yet its precise role in plant immunity remained unclear. Recent studies suggest that E3 ligases like SlATL2 could be critical in balancing immune responses. Given the complexity of plant immune signaling, there is a pressing need to investigate how these regulatory mechanisms influence plant-pathogen interactions.
The study, published (DOI: 10.1093/hr/uhaf078) in Horticulture Research (March 2025), conducted by researchers at Zhejiang University, explores how SlATL2 affects tomato immunity against Pseudomonas syringae DC3000. By using CRISPR-Cas9 gene editing and other molecular tools, the research demonstrates that SlATL2 suppresses immune responses by facilitating the degradation of SlCSN5a, a key regulator in the plant's defense mechanism. These findings offer novel insights into the molecular mechanisms governing tomato immunity and suggest potential strategies for improving disease resistance in crops.
The study shows that SlATL2 negatively regulates tomato immunity by promoting the ubiquitination and degradation of SlCSN5a, a critical component of the COP9 signalosome (CSN). SlATL2 expression is induced during infection with Pst DC3000 and upon treatment with defense hormones like salicylic acid (SA) and jasmonic acid (JA). Using mutant lines and overexpression plants, the researchers demonstrated that silencing SlATL2 enhances resistance to Pst DC3000, with decreased bacterial growth and smaller lesion sizes in the leaves. In contrast, SlATL2 overexpression plants exhibited more severe disease symptoms. The study also revealed that SlATL2-mediated degradation of SlCSN5a reduces reactive oxygen species (ROS) production and callose deposition, key defense responses during infection. Furthermore, SlATL2 silencing increased the expression of SA-related defense genes, highlighting the involvement of SA signaling in this regulatory pathway. These findings suggest that SlATL2 functions as a negative regulator in tomato immunity, providing new targets for genetic improvement of disease resistance in crops.
"These findings underscore the importance of post-translational modifications in regulating plant immune responses," said Dr. Dayong Li, a co-author of the study. "By targeting SlCSN5a for degradation, SlATL2 dampens immune activation, providing a pathway that could be manipulated to enhance crop resistance to bacterial pathogens. Our research opens up new strategies for breeding plants with more robust immune systems, ultimately contributing to global food security."
The insights gained from this study have broad implications for improving disease resistance in crops. By targeting SlATL2, it may be possible to enhance tomato resistance to bacterial pathogens like Pseudomonas syringae. Additionally, this research provides a framework for exploring similar E3 ligases in other crops, offering a potential strategy for genetic engineering aimed at boosting immune responses. Furthermore, understanding the molecular mechanisms behind SlATL2’s regulation of immune responses could help reduce dependency on chemical pesticides, contributing to more sustainable agricultural practices.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhaf078
Funding information
This research was supported by the National Natural Science Foundation of China under grant no. 31972415 and the Zhejiang Provincial Natural Science Foundation of China under grant no. LY21C140003.
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.