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A Xanthomonas uridine 5′-monophosphate transferase inhibits plant immune kinases


Plant innate immunity is activated on the detection of pathogen-associated molecular patterns (PAMPs) at the cell surface, or of pathogen effector proteins inside the plant cell1,2,3,4. Together, PAMP-triggered immunity and effector-triggered immunity constitute powerful defences against various phytopathogens. Pathogenic bacteria inject a variety of effector proteins into the host cell to assist infection or propagation. A number of effector proteins have been shown to inhibit plant immunity5, but the biochemical basis remains unknown for the vast majority of these effectors. Here we show that the Xanthomonas campestris pathovar campestris type III effector AvrAC enhances virulence and inhibits plant immunity by specifically targeting Arabidopsis BIK1 and RIPK, two receptor-like cytoplasmic kinases known to mediate immune signalling6,7,8. AvrAC is a uridylyl transferase that adds uridine 5′-monophosphate to and conceals conserved phosphorylation sites in the activation loop of BIK1 and RIPK, reducing their kinase activity and consequently inhibiting downstream signalling.

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Figure 1: AvrAC inhibits plant immunity.
Figure 2: AvrAC targets BIK1 and inhibits early PTI signalling events.
Figure 3: AvrAC uridylylates BIK1 and RIPK.
Figure 4: AvrAC uridylyl transferase activity and BIK1 are required for AvrAC virulence in plants.


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The authors thank J. Chai for sharing plasmids before publication, A. Bent for the XccB186 strain, S. Y. He and F. White for helpful comments. J.-M.Z. was supported by grants from the Chinese Ministry of Science and Technology (2011CB100700; 2010CB835301). S.C. was supported by a grant from the Chinese Ministry of Science and Technology (2010CB835204) C.H. was supported by Funds from Hainan University.

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S.C., C.H. and J.-M.Z. conceived and designed the experiments. F.F., F.Y., W.R., X.W. and J.Z. performed the experiments. F.F., F.Y., S.C., C.H. and J.-M.Z. analysed the data. F.F., S.C., C.H. and J.-M.Z. wrote the paper.

Corresponding authors

Correspondence to Chaozu He or Jian-Min Zhou.

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The authors declare no competing financial interests.

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Feng, F., Yang, F., Rong, W. et al. A Xanthomonas uridine 5′-monophosphate transferase inhibits plant immune kinases. Nature 485, 114–118 (2012).

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