Plants rely on complex internal networks to defend themselves against microbial invaders. One such network is ubiquitination, where enzymes called E3 ligases tag other proteins to control their fate—be it degradation or relocation. At the same time, chloroplasts are being redefined beyond their classic role in photosynthesis, now seen as key players in producing immune signals like salicylic acid and jasmonic acid. However, the precise link between ubiquitin tagging and chloroplast-driven defense remains murky. Due to these unresolved connections, there is a pressing need to explore how targeted protein movement influences plant immune responses.
In a study (DOI: 10.1093/hr/uhae241) led by researchers at Huazhong Agricultural University, scientists identified a new molecular pathway that boosts potato immunity. Published on August 30, 2024, in Horticulture Research, the paper reveals how the enzyme StRFP1 facilitates the chloroplast accumulation of the transporter StGPT1 by tagging it with ubiquitin at the endoplasmic reticulum. This repositioning boosts defense signaling, helping the plant fight off Phytophthora infestans, the fungus behind late blight. The discovery opens new possibilities for strengthening crop resilience through precise control of intracellular protein dynamics.
Through a series of molecular and cellular experiments, the team discovered that StGPT1 interacts directly with StRFP1, an E3 ligase previously linked to pathogen resistance. Fluorescent imaging revealed that StGPT1 normally shuttles between the endoplasmic reticulum and the chloroplast. However, when StRFP1 is present, it tags StGPT1 with ubiquitin at the ER, resulting in its buildup within chloroplasts—where immune hormones and defense signals are produced. Overexpressing StGPT1 in both potato and tobacco plants significantly reduced infection severity, while silencing it led to weakened immunity and stunted growth.
Importantly, the defense effect depended on StGPT1 reaching the chloroplast. Mutants that failed to localize there lost their resistance capabilities. Plants with both proteins co-expressed showed even stronger disease protection, suggesting a synergistic relationship. Moreover, expression of immune-related genes and production of ROS, salicylic acid, and jasmonic acid were significantly elevated in the presence of chloroplast-localized StGPT1. This demonstrates that the transporter is not just a cargo mover—it's a crucial switch in the plant's immune system.
“This research reveals a surprising twist in the story of protein ubiquitination,” said Dr. Zhendong Tian, lead author of the study. “Rather than marking StGPT1 for destruction, StRFP1 helps it reach its immune-boosting destination. This shows how selective tagging of proteins can fine-tune plant defenses at the subcellular level—something we can potentially harness in agricultural biotechnology.”
Understanding how StGPT1 and StRFP1 cooperate could lead to more resilient crop varieties through targeted genetic strategies. By promoting the accumulation of key transporters in the chloroplast, breeders and researchers may enhance natural immunity without compromising growth. Since this mechanism involves core processes shared across many plant species, the approach might extend beyond potatoes to other crops threatened by fungal diseases. Ultimately, this work lays the foundation for designing smarter, molecular-based interventions in sustainable agriculture.
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References
DOI
10.1093/hr/uhae241
Original Source URL
https://doi.org/10.1093/hr/uhae241
Funding information
This project was supported by 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.