Structure–function analysis of ZAR1 immune receptor reveals key molecular interactions for activity

• Published in: The Plant journal : for cell and molecular biology Vol. 101; no. 2; pp. 352 - 370
• Main Authors: Baudin, Maël, Schreiber, Karl J., Martin, Eliza C., Petrescu, Andrei J., Lewis, Jennifer D.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.01.2020
• Subjects: Activation; Antigen-antibody complexes; Arabidopsis Proteins; Bacterial Proteins - metabolism; Carrier Proteins - chemistry; Carrier Proteins - genetics; Carrier Proteins - metabolism; cell death; coiled‐coil domain; effector proteins; Function analysis; hypersensitive response; Immune response; Kinases; Leucine; Models, Molecular; Molecular interactions; Nicotiana - genetics; Nicotiana - immunology; Nicotiana - metabolism; Nicotiana benthamiana; NLR; Nucleotides; nucleotide‐binding [NB] leucine‐rich repeat [LRR] receptor; Pathogens; Phosphotransferases - metabolism; Plant Immunity - physiology; Plant Proteins - metabolism; Protein Conformation; Protein Interaction Domains and Motifs; Proteins; Pseudomonas syringae; Pseudomonas syringae - metabolism; structural modelling; Structure-function relationships; Xanthomonas - metabolism; effector proteins; hypersensitive response; Nicotiana benthamiana; coiled-coil domain; cell death; Pseudomonas syringae; NLR; nucleotide-binding [NB] leucine-rich repeat [LRR] receptor; structural modelling; molecular interactions
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.14547

Summary NLR (nucleotide‐binding [NB] leucine‐rich repeat [LRR] receptor) proteins are critical for inducing immune responses in response to pathogen proteins, and must be tightly modulated to prevent spurious activation in the absence of a pathogen. The ZAR1 NLR recognizes diverse effector proteins from Pseudomonas syringae, including HopZ1a, and Xanthomonas species. Receptor‐like cytoplasmic kinases (RLCKs) such as ZED1, interact with ZAR1 and provide specificity for different effector proteins, such as HopZ1a. We previously developed a transient expression system in Nicotiana benthamiana that allowed us to demonstrate that ZAR1 function is conserved from the Brassicaceae to the Solanaceae. Here, we combined structural modelling of ZAR1, with molecular and functional assays in our transient system, to show that multiple intramolecular and intermolecular interactions modulate ZAR1 activity. We identified determinants required for the formation of the ZARCC oligomer and its activity. Lastly, we characterized intramolecular interactions between ZAR1 subdomains that participate in keeping ZAR1 immune complexes inactive. This work identifies molecular constraints on immune receptor function and activation. Significance Statement Immune receptors must be carefully modulated to prevent spurious activation in the absence of pathogens. Structure‐informed analyses reveal multiple finely tuned intramolecular interactions that modulate the activity of the immune receptor ZAR1.