A natural diversity screen in Arabidopsis thaliana reveals determinants for HopZ1a recognition in the ZAR1‐ZED1 immune complex

• Published in: Plant, cell and environment Vol. 44; no. 2; pp. 629 - 644
• Main Authors: Baudin, Maël, Martin, Eliza C., Sass, Chodon, Hassan, Jana A., Bendix, Claire, Sauceda, Rolin, Diplock, Nathan, Specht, Chelsea D., Petrescu, Andrei J., Lewis, Jennifer D.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.02.2021; Wiley Subscription Services, Inc
• Subjects: Arabidopsis thaliana; Computer applications; Ecotypes; Evolutionary genetics; Genomes; HopZ1a; Immune response; Immune system; Innate immunity; Kinases; Leucine; natural diversity; NLR; Nucleotides; Pathogens; plant immunity; protein–protein interaction; Pseudomonas syringae; Receptors; Recognition; type III secreted effector; ZAR1; ZED1; Arabidopsis thaliana; ZED1; type III secreted effector; NLR; Pseudomonas syringae; protein-protein interaction; natural diversity; HopZ1a; plant immunity; ZAR1
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.13927

Pathogen pressure on hosts can lead to the evolution of genes regulating the innate immune response. By characterizing naturally occurring polymorphisms in immune receptors, we can better understand the molecular determinants of pathogen recognition. ZAR1 is an ancient Arabidopsis thaliana NLR (Nucleotide‐binding [NB] Leucine‐rich‐repeat [LRR] Receptor) that recognizes multiple secreted effector proteins from the pathogenic bacteria Pseudomonas syringae and Xanthomonas campestris through its interaction with receptor‐like cytoplasmic kinases (RLCKs). ZAR1 was first identified for its role in recognizing P. syringae effector HopZ1a, through its interaction with the RLCK ZED1. To identify additional determinants of HopZ1a recognition, we performed a computational screen for ecotypes from the 1001 Genomes project that were likely to lack HopZ1a recognition, and tested ~300 ecotypes. We identified ecotypes containing polymorphisms in ZAR1 and ZED1. Using our previously established Nicotiana benthamiana transient assay and Arabidopsis ecotypes, we tested for the effect of naturally occurring polymorphisms on ZAR1 interactions and the immune response. We identified key residues in the NB or LRR domain of ZAR1 that impact the interaction with ZED1. We demonstrate that natural diversity combined with functional assays can help define the molecular determinants and interactions necessary to regulate immune induction in response to pathogens. Using genetic diversity of Arabidopsis thaliana and complementation assays in Nicotiana benthamiana, we characterized molecular and functional constraints on immunity to further understand the ancient and conserved immune receptor ZAR1 and its recognition of different pathogenic effector proteins.