Abstract
The Pseudomonas syringae acetyltransferase HopZ1a is delivered into host cells by the type III secretion system to promote bacterial growth. However, in the model plant host Arabidopsis thaliana, HopZ1a activity results in an effector-triggered immune response (ETI) that limits bacterial proliferation. HopZ1a-triggered immunity requires the nucleotide-binding, leucine-rich repeat domain (NLR) protein, ZAR1, and the pseudokinase, ZED1. Here we demonstrate that HopZ1a can acetylate members of a family of 'receptor-like cytoplasmic kinases' (RLCK family VII; also known as PBS1-like kinases, or PBLs) and promote their interaction with ZED1 and ZAR1 to form a ZAR1-ZED1-PBL ternary complex. Interactions between ZED1 and PBL kinases are determined by the pseudokinase features of ZED1, and mutants designed to restore ZED1 kinase motifs can (1) bind to PBLs, (2) recruit ZAR1, and (3) trigger ZAR1-dependent immunity in planta, all independently of HopZ1a. A ZED1 mutant that mimics acetylation by HopZ1a also triggers immunity in planta, providing evidence that effector-induced perturbations of ZED1 also activate ZAR1. Overall, our results suggest that interactions between these two RLCK families are promoted by perturbations of structural features that distinguish active from inactive kinase domain conformations. We propose that effector-induced interactions between ZED1/ZRK pseudokinases (RLCK family XII) and PBL kinases (RLCK family VII) provide a sensitive mechanism for detecting perturbations of either kinase family to activate ZAR1-mediated ETI.
Publication types
-
Research Support, Non-U.S. Gov't
MeSH terms
-
Acetylation
-
Arabidopsis / genetics
-
Arabidopsis / immunology*
-
Arabidopsis / metabolism*
-
Arabidopsis Proteins / chemistry
-
Arabidopsis Proteins / genetics
-
Arabidopsis Proteins / immunology*
-
Arabidopsis Proteins / metabolism*
-
Bacterial Proteins / chemistry
-
Bacterial Proteins / metabolism
-
Carrier Proteins / chemistry
-
Carrier Proteins / immunology
-
Carrier Proteins / metabolism
-
Host Microbial Interactions / genetics
-
Host Microbial Interactions / immunology
-
Models, Immunological
-
Mutation
-
Phosphotransferases / genetics
-
Phosphotransferases / immunology*
-
Phosphotransferases / metabolism*
-
Plant Immunity*
-
Protein Interaction Domains and Motifs
-
Protein Kinases / chemistry
-
Protein Kinases / metabolism
-
Pseudomonas syringae / immunology
-
Pseudomonas syringae / metabolism
-
Pseudomonas syringae / pathogenicity
Substances
-
Arabidopsis Proteins
-
Bacterial Proteins
-
Carrier Proteins
-
ZAR1 protein, Arabidopsis
-
ZED1 protein, Arabidopsis
-
Phosphotransferases
-
Protein Kinases
Grants and funding
This work was supported by Natural Sciences and Engineering Research Council of Canada (
http://www.nserc-crsng.gc.ca/index_eng.asp) Discovery Grants (D.S.G and D.D.), Natural Sciences and Engineering Research Council of Canada Postgraduate Awards (D.S. and A.M.), Canada Research Chairs (
http://www.chairs-chaires.gc.ca/home-accueil-eng.aspx) in Comparative Genomics (D.S.G.) and Plant-Microbe Systems Biology (D.D.), and the Center for the Analysis of Genome Evolution and Function (
https://www.cagef.utoronto.ca/; D.S.G. and D.D.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.