Type III effector activation via nucleotide binding, phosphorylation, and host target interaction.
The Pseudomonas syringae type III effector protein avirulence protein B (AvrB) is delivered into plant cells, where it targets the Arabidopsis RIN4 protein (resistance to Pseudomonas maculicula protein 1 [RPM1]-interacting protein). RIN4 is a regulator of basal host defense responses. Targeting of RIN4 by AvrB is recognized by the host RPM1 nucleotide-binding leucine-rich repeat disease resistance protein, leading to accelerated defense responses, cessation of pathogen growth, and hypersensitive host cell death at the infection site. We determined the structure of AvrB complexed with an AvrB-binding fragment of RIN4 at 2.3 A resolution. We also determined the structure of AvrB in complex with adenosine diphosphate bound in a binding pocket adjacent to the RIN4 binding domain. AvrB residues important for RIN4 interaction are required for full RPM1 activation. AvrB residues that contact adenosine diphosphate are also required for initiation of RPM1 function. Nucleotide-binding residues of AvrB are also required for its phosphorylation by an unknown Arabidopsis protein(s). We conclude that AvrB is activated inside the host cell by nucleotide binding and subsequent phosphorylation and, independently, interacts with RIN4. Our data suggest that activated AvrB, bound to RIN4, is indirectly recognized by RPM1 to initiate plant immune system function.
Desveaux
Darrell
D
Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America.
Singer
Alex U
AU
Wu
Ai-Jiuan
AJ
McNulty
Brian C
BC
Musselwhite
Laura
L
Nimchuk
Zachary
Z
Sondek
John
J
Dangl
Jeffery L
JL
D017360:Arabidopsis / Q000235:genetics / Q000276:immunology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism; D018744:DNA, Plant / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D018506:Gene Expression Regulation, Plant; D016905:Gram-Negative Bacterial Infections / Q000276:immunology; D007113:Immunity, Innate / Q000276:immunology; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D010766:Phosphorylation; D044224:Pseudomonas syringae / Q000235:genetics / Q000472:pathogenicity*
D029681:Arabidopsis Proteins; C100931:AvrB protein, Pseudomonas syringae; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D018744:DNA, Plant; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; C453279:RIN4 protein, Arabidopsis; C095014:RPM1 protein, Arabidopsis