Pseudomonas syringae type III effector HopAF1 suppresses plant immunity by targeting methionine recycling to block ethylene induction.
HopAF1 is a type III effector protein of unknown function encoded in the genomes of several strains of Pseudomonas syringae and other plant pathogens. Structural modeling predicted that HopAF1 is closely related to deamidase proteins. Deamidation is the irreversible substitution of an amide group with a carboxylate group. Several bacterial virulence factors are deamidases that manipulate the activity of specific host protein substrates. We identified Arabidopsis methylthioadenosine nucleosidase proteins MTN1 and MTN2 as putative targets of HopAF1 deamidation. MTNs are enzymes in the Yang cycle, which is essential for the high levels of ethylene biosynthesis in Arabidopsis We hypothesized that HopAF1 inhibits the host defense response by manipulating MTN activity and consequently ethylene levels. We determined that bacterially delivered HopAF1 inhibits ethylene biosynthesis induced by pathogen-associated molecular patterns and that Arabidopsis mtn1 mtn2 mutant plants phenocopy the effect of HopAF1. Furthermore, we identified two conserved asparagines in MTN1 and MTN2 from Arabidopsis that confer loss of function phenotypes when deamidated via site-specific mutation. These residues are potential targets of HopAF1 deamidation. HopAF1-mediated manipulation of Yang cycle MTN proteins is likely an evolutionarily conserved mechanism whereby HopAF1 orthologs from multiple plant pathogens contribute to disease in a large variety of plant hosts.
Department of Biology, University of North Carolina, Chapel Hill, NC 27599;
Erica J
EJ
Washington
Department of Biology, University of North Carolina, Chapel Hill, NC 27599;
M Shahid
MS
Mukhtar
Department of Biology, University of North Carolina, Chapel Hill, NC 27599;
Omri M
OM
Finkel
Department of Biology, University of North Carolina, Chapel Hill, NC 27599;
Li
L
Wan
Department of Biological Chemistry, John Innes Centre, Norwich NR4 7UH, United Kingdom;
Mark J
0000-0001-8921-3835
MJ
Banfield
Department of Biology, University of North Carolina, Chapel Hill, NC 27599;
Joseph J
JJ
Kieber
Department of Biology, University of North Carolina, Chapel Hill, NC 27599; Howard Hughes Medical Institute, University of North Carolina, Chapel Hill, NC 27599; Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599; Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, NC 27599; Carolina Center for Genome Sciences, University of North Carolina, Chapel Hill, NC 27599 dangl@email.unc.edu.
Jeffery L
JL
Dangl
D000215:Acylation; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000276:immunology / Q000382:microbiology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology*; D020134:Catalytic Domain; D002462:Cell Membrane / Q000378:metabolism; D005030:Ethylenes / Q000037:antagonists & inhibitors*; D019143:Evolution, Molecular; D020440:Gene Duplication; D008715:Methionine / Q000378:metabolism*; D010802:Phylogeny; D044224:Pseudomonas syringae / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D005030:Ethylenes; C036216:ethylene; D008715:Methionine
Pseudomonas syringae; Yang cycle; ethylene; plant immune system; type III effectors