title: AvrRpm1 missense mutations weakly activate RPS2-mediated immune response in Arabidopsis thaliana.
abstract: Plants recognize microbes via specific pattern recognition receptors that are activated by microbe-associated molecular patterns (MAMPs), resulting in MAMP-triggered immunity (MTI). Successful pathogens bypass MTI in genetically diverse hosts via deployment of effectors (virulence factors) that inhibit MTI responses, leading to pathogen proliferation. Plant pathogenic bacteria like Pseudomonas syringae utilize a type III secretion system to deliver effectors into cells. These effectors can contribute to pathogen virulence or elicit disease resistance, depending upon the host plant genotype. In disease resistant genotypes, intracellular immune receptors, typically belonging to the nucleotide binding leucine-rich repeat family of proteins, perceive bacterial effector(s) and initiate downstream defense responses (effector triggered immunity) that include the hypersensitive response, and transcriptional re-programming leading to various cellular outputs that collectively halt pathogen growth. Nucleotide binding leucine-rich repeat sensors can be indirectly activated via perturbation of a host protein acting as an effector target. AvrRpm1 is a P. syringae type III effector. Upon secretion into the host cell, AvrRpm1 is acylated by host enzymes and directed to the plasma membrane, where it contributes to virulence. This is correlated with phosphorylation of Arabidopsis RIN4 in vivo. RIN4 is a negative regulator of MAMP-triggered immunity, and its modification in the presence of four diverse type III effectors, including AvrRpm1, likely enhances this RIN4 regulatory function. The RPM1 nucleotide binding leucine-rich repeat sensor perceives RIN4 perturbation in disease resistant plants, leading to a successful immune response. Here, demonstrate that AvrRpm1 has a fold homologous to the catalytic domain of poly(ADP-ribosyl) polymerase. Site-directed mutagenesis of each residue in the putative catalytic triad, His63-Tyr122-Asp185 of AvrRpm1, results in loss of both AvrRpm1-dependent virulence and AvrRpm1-mediated activation of RPM1, but, surprisingly, causes a gain of function: the ability to activate the RPS2 nucleotide binding leucine-rich repeat sensor.
authors.affiliation: Department of Biology, University of North Carolina, Chapel Hill, North Carolina, United States of America.
authors.forename: Karen A
authors.initials: KA
authors.lastname: Cherkis
authors.forename: Brenda R S
authors.initials: BR
authors.lastname: Temple
authors.forename: Eui-Hwan
authors.initials: EH
authors.lastname: Chung
authors.forename: John
authors.initials: J
authors.lastname: Sondek
authors.forename: Jeffery L
authors.initials: JL
authors.lastname: Dangl
mesh_terms: D036002:ADP Ribose Transferases / Q000378:metabolism; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D017360:Arabidopsis / Q000276:immunology* / Q000382:microbiology*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D055162:Biocatalysis; D002352:Carrier Proteins / Q000378:metabolism; D017124:Conserved Sequence; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D020125:Mutation, Missense / Q000235:genetics*; D057865:Plant Immunity / Q000276:immunology*; D011065:Poly(ADP-ribose) Polymerases / Q000737:chemistry; D044224:Pseudomonas syringae / Q000472:pathogenicity; D040681:Structural Homology, Protein; D013329:Structure-Activity Relationship; D014774:Virulence
chemical_list: D000596:Amino Acids; D029681:Arabidopsis Proteins; C502082:AvrRpm1 protein, Pseudomonas syringae; D001426:Bacterial Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C453279:RIN4 protein, Arabidopsis; C089426:RPS2 protein, Arabidopsis; C420919:avrRpt2 protein, Pseudomonas syringae; D036002:ADP Ribose Transferases; D011065:Poly(ADP-ribose) Polymerases