A type III effector ADP-ribosylates RNA-binding proteins and quells plant immunity

Nature. 2007 May 17;447(7142):284-8. doi: 10.1038/nature05737. Epub 2007 Apr 22.


The bacterial plant pathogen Pseudomonas syringae injects effector proteins into host cells through a type III protein secretion system to cause disease. The enzymatic activities of most of P. syringae effectors and their targets remain obscure. Here we show that the type III effector HopU1 is a mono-ADP-ribosyltransferase (ADP-RT). HopU1 suppresses plant innate immunity in a manner dependent on its ADP-RT active site. The HopU1 substrates in Arabidopsis thaliana extracts were RNA-binding proteins that possess RNA-recognition motifs (RRMs). A. thaliana knockout lines defective in the glycine-rich RNA-binding protein GRP7 (also known as AtGRP7), a HopU1 substrate, were more susceptible than wild-type plants to P. syringae. The ADP-ribosylation of GRP7 by HopU1 required two arginines within the RRM, indicating that this modification may interfere with GRP7's ability to bind RNA. Our results suggest a pathogenic strategy where the ADP-ribosylation of RNA-binding proteins quells host immunity by affecting RNA metabolism and the plant defence transcriptome.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • ADP Ribose Transferases / metabolism*
  • Adenosine Diphosphate Ribose / metabolism
  • Arabidopsis / genetics
  • Arabidopsis / immunology
  • Arabidopsis / metabolism
  • Arabidopsis / microbiology
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Immunity, Innate / genetics
  • Immunity, Innate / immunology
  • Mutation / genetics
  • Peptides / metabolism
  • Plant Diseases / genetics
  • Plant Diseases / immunology*
  • Plant Diseases / microbiology*
  • Pseudomonas syringae / enzymology*
  • Pseudomonas syringae / immunology
  • Pseudomonas syringae / pathogenicity*
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism*
  • Substrate Specificity
  • Tobacco / metabolism
  • Virulence


  • ATGRP7 protein, Arabidopsis
  • Arabidopsis Proteins
  • Peptides
  • RNA-Binding Proteins
  • Adenosine Diphosphate Ribose
  • polyarginine
  • ADP Ribose Transferases