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Research Project: Mining Collections of Wild Germplasm and Novel Defense Regulators for Enhanced Plant Defenses

Location: Plant Gene Expression Center

Title: Structure-function analysis of ZAR1 immune receptor reveals key molecular interactions for activity

item BAUDIN, MAEL - University Of California
item SCHREIBER, KARL - University Of California
item MARTIN, ELIZA - University Of California
item PETRESCU, ANDREI - University Of California
item Lewis, Jennifer

Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2019
Publication Date: 9/26/2019
Citation: Baudin, M., Schrieber, K., Martin, E.C., Petrescu, A.J., Lewis, J.D. 2019. Structure-function analysis of ZAR1 immune receptor reveals key molecular interactions for activity. Plant Journal. 101(2):352-370.

Interpretive Summary: Plants have developed a sensitive surveillance system to detect modification of their own proteins by pathogens. This surveillance system must be exquisitely fine-tuned to prevent activity in the absence of a pathogen, and to activate extremely rapidly once the pathogen is detected. We previously identified a plant pseudokinase that works with a resistance protein to act as a “mousetrap” for recognition of a bacterial effector protein. We developed a transient expression system in Nicotiana benthamiana that demonstrated the resistance protein was active in diverse plant families. This system allowed us to identify key requirements for immune receptor function and activation. By identifying the molecular requirements for effector recognition, this work will aid in informing the rational design of a decoy protein for recognition of other pathogens or effector proteins.

Technical Abstract: 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 ZAR1 function is conserved from the Brassicaceae to the Solanaceae. Here, we combined structural modeling 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.