Late blight, caused by P. infestans, remains one of the most devastating diseases in potato production worldwide. Traditional breeding and chemical control often fall short due to the pathogen's rapid evolution and environmental concerns over fungicide use. In plants, chloroplasts are not only sites of photosynthesis but also hubs for defense signaling, producing ROS and hormones like JA and SA. E3 ubiquitin ligases regulate protein stability, localization, and activity, often influencing immunity. While the E3 ligase StRFP1 was previously shown to improve blight resistance, its mode of action was unclear. Based on these challenges, there is a need to explore how protein trafficking and ubiquitination coordinate chloroplast-mediated defense responses.
Wuhan, China — August 30, 2024 — Researchers at Huazhong Agricultural University have uncovered how a potato transporter protein, StGPT1, and the E3 ubiquitin ligase StRFP1 cooperate to bolster resistance against Phytophthora infestans. Published (DOI: 10.1093/hr/uhae241) in Horticulture Research, the study reveals that StRFP1 binds to StGPT1 on the endoplasmic reticulum and promotes its accumulation in chloroplasts, where it triggers robust immune responses. This previously unknown mechanism underscores the importance of subcellular protein localization in plant defense and opens new avenues for breeding late blight–resistant potato varieties.
Through yeast two-hybrid screening, StGPT1 was identified as a binding partner of StRFP1. Fluorescence imaging showed StGPT1 is dually localized to chloroplasts and the ER, mirroring its Arabidopsis homolog. Overexpression in potato and N. benthamiana reduced lesion size after P. infestans infection, whereas silencing increased susceptibility and impaired growth. Biochemical assays revealed that StRFP1 ubiquitinates StGPT1 on the ER, but instead of promoting degradation, this process favored the accumulation of its mature chloroplast form. Functional assays demonstrated that chloroplast localization is essential for StGPT1’s defensive role. Overexpression lines displayed heightened ROS bursts, elevated JA and SA levels, and upregulated PAMP-triggered immunity (PTI) marker genes such as StWRKY7, StWRKY8, StACRE31, and StPti5. Co-expression of StGPT1 and StRFP1 in leaves led to significantly stronger resistance than either protein alone, indicating a synergistic defense effect. The results suggest that StRFP1-mediated ubiquitination modifies StGPT1 trafficking to chloroplasts, enhancing its immune signaling function and fortifying the plant against late blight.
“Our work uncovers an unconventional role for ubiquitination — not as a signal for protein destruction, but as a means to direct a key transporter into chloroplasts, where it can activate plant immune responses,” said corresponding author Dr. Zhendong Tian. “By elucidating the cooperative action of StGPT1 and StRFP1, we reveal a new layer of regulation in plant-pathogen interactions. This knowledge not only deepens our understanding of chloroplast-based defense but also offers promising molecular targets for developing potato varieties with durable late blight resistance.”
The discovery of the StGPT1–StRFP1 interaction mechanism has significant implications for sustainable agriculture. By leveraging this dual-targeting pathway, breeders could develop potato cultivars with enhanced resistance to late blight without relying on intensive fungicide applications. The findings also highlight the broader potential of manipulating protein localization and ubiquitination to strengthen plant defenses across crops. Given that GPT1 homologs exist in many plant species, similar strategies could be applied to improve resilience against other pathogens. This approach aligns with global efforts to enhance food security while reducing the environmental footprint of disease management in agriculture.
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References
DOI
10.1093/hr/uhae241
Original Source URL
https://doi.org/10.1093/hr/uhae241
Funding information
We are grateful for financial support from the National Key R&D Program of China (grants No. 2023YFF1000404) and the National Natural Science Foundation of China (grants No. 32372172, 32072121, 31761143007).
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.