The Xanthomonas campestris type III effector XopJ proteolytically degrades proteasome subunit RPT6.
Many animal and plant pathogenic bacteria inject type III effector (T3E) proteins into their eukaryotic host cells to suppress immunity. The Yersinia outer protein J (YopJ) family of T3Es is a widely distributed family of effector proteins found in both animal and plant pathogens, and its members are highly diversified in virulence functions. Some members have been shown to possess acetyltransferase activity; however, whether this is a general feature of YopJ family T3Es is currently unknown. The T3E Xanthomonas outer protein J (XopJ), a YopJ family effector from the plant pathogen Xanthomonas campestris pv vesicatoria, interacts with the proteasomal subunit Regulatory Particle AAA-ATPase6 (RPT6) in planta to suppress proteasome activity, resulting in the inhibition of salicylic acid-related immune responses. Here, we show that XopJ has protease activity to specifically degrade RPT6, leading to reduced proteasome activity in the cytoplasm as well as in the nucleus. Proteolytic degradation of RPT6 was dependent on the localization of XopJ to the plasma membrane as well as on its catalytic triad. Mutation of the Walker B motif of RPT6 prevented XopJ-mediated degradation of the protein but not XopJ interaction. This indicates that the interaction of RPT6 with XopJ is dependent on the ATP-binding activity of RPT6, but proteolytic cleavage additionally requires its ATPase activity. Inhibition of the proteasome impairs the proteasomal turnover of Nonexpressor of Pathogenesis-Related1 (NPR1), the master regulator of salicylic acid responses, leading to the accumulation of ubiquitinated NPR1, which likely interferes with the full induction of NPR1 target genes. Our results show that YopJ family T3Es are not only highly diversified in virulence function but also appear to possess different biochemical activities.
Plant Metabolism Group, Leibniz Institute of Vegetable and Ornamental Crops, 14979 Grossbeeren, Germany (S.Ü., F.B.);Friedrich-Alexander-University Erlangen-Nuremberg, Department of Biology, Division of Biochemistry, 91058 Erlangen, Germany (S.Ü., F.B.); andInstitut of Biochemistry and Biology, University of Potsdam, 14476 Potsdam, Germany (F.B.) uestuen@igzev.de boernke@igzev.de.
Suayib
http://orcid.org/0000-0002-8049-296X
S
Üstün
Plant Metabolism Group, Leibniz Institute of Vegetable and Ornamental Crops, 14979 Grossbeeren, Germany (S.Ü., F.B.);Friedrich-Alexander-University Erlangen-Nuremberg, Department of Biology, Division of Biochemistry, 91058 Erlangen, Germany (S.Ü., F.B.); andInstitut of Biochemistry and Biology, University of Potsdam, 14476 Potsdam, Germany (F.B.) uestuen@igzev.de boernke@igzev.de.
Frederik
http://orcid.org/0000-0003-3558-0482
F
Börnke
D000074183:ATPases Associated with Diverse Cellular Activities; D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000378:metabolism*; D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000378:metabolism*; D058947:Bacterial Secretion Systems; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D060588:LIM Domain Proteins / Q000737:chemistry / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D055550:Protein Stability; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism*; D059748:Proteolysis; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D016959:Xanthomonas campestris / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D060588:LIM Domain Proteins; C092282:PSMC5 protein, human; D021122:Protein Subunits; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D046988:Proteasome Endopeptidase Complex; D000074183:ATPases Associated with Diverse Cellular Activities