When plants are attacked by pathogens, plants activate the body’s immune response through the NPR1 (NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1) protein within the cell, which in turn protects plant growth.
The NPR1 protein is a major plant immunomodulator that regulates the expression of more than 2,000 genes associated with plant immunity. Although NPR1 plays a very important role in plant defense, the three-dimensional structure of NPR1 has been unknown. While scientists have also been working to investigate how this protein provides protection for plants, acquiring npr1’s three-dimensional structure is key to gaining a deeper understanding of how npr1 proteins regulate the mechanisms of plant immunity.
On May 11, 2022, Nature Online published a three-dimensional spatial structure of the first Arabidopsis thaliana NPR1 protein and npr1 protein complex with transcription factor TGA3, elucidating the transcriptional regulation mechanism of NPR1 anti-pathogen genes under salicylate induction.
Professor Pei Zhou of the Department of Biochemistry and Professor Xinnian Dong of the Department of Biology of Duke University School of Medicine are the co-corresponding authors of the article, and Research Assistants Dr. Shivesh Kumar, Dr. Raul Zavaliev, and Dr. Qinglin Wu are the co-first authors of the paper.
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Figure 1. Arabidopsis NPR1 cryo-EM structure.
The team of Professors Zhou and Dong used single-particle cryo-EM technology and X-ray crystallography to resolve the three-dimensional structure of Arabidopsis thaliana NPR1. NPR1 is a flying eagle-shaped homologous dimer composed of BTB domains, BHB domains (BTB and carboxyterminal Kelch helix bundle), 4 ankyrin domains, and a flexible salicylic acid combined domain. The crystal structure of NPR1 also found that its BTB domain contained a unique zinc finger structure, and revealed that this zinc finger structure plays an important role in the interaction and NPR1 polymerization of the BTB domain and the ankyrin domain.
Figure 2. NPR1-TGA3 complex cryo-EM structure
The study also reported on the cryo-EM structure of a complex of Arabidopsis NPR1 and transcription factor TGA3. This complex structure clearly shows that the dimer NPR1 forms a transcriptional enhancer by bridging the dimers of two TGA3s. In addition, the researchers successfully captured the CONFORMation of the NPR12-TGA32 complex in addition to TGA32-NPR12-TGA32, and proposed that this step-by-step assembly process may reflect a model of how NPR1 binds to homologous or heterologous transcripts to regulate gene transcription that resists pathogenic bacteria. They validated this model by using electrophoretic migration analysis and genetic data analysis.
Figure 3. Dimer NPR1 bridges an enhancer model of two dimer TGA transcription factors
Ever since growing crops, humans have begun to fight numerous pests and pathogens that hinder plant growth. For example, the water mold potato late blight (Phytophthora infestans) caused 1 million deaths and 2 million refugees homeless during the 18th-century Irish potato famine. It has been 25 years since its discovery. This study is the first to report the high-resolution three-dimensional structure of NPR1 and elucidate the gene transcription mechanism of NPR1 regulation of pathogenic bacteria at the molecular level. Understanding how this protein works and how it interacts in synergy with other molecules could help researchers design better crops, which is important for greatly enhancing the disease resistance of plants. (Source: Science Network)
Related paper information:https://doi.org/10.1038/s41586-022-04699-w