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Keywords:

  • AvrB;
  • bacterial blight;
  • Pseudomonas syringae ;
  • resistance protein;
  • RIN4;
  • soybean (Glycine max)

Summary

  • The Pseudomonas syringae effector AvrB interacts with four related soybean (Glycine max) proteins (GmRIN4a–d), three (GmRIN4b, c, d) of which also interact with the cognate resistance (R) protein, Rpg1-b. Here, we investigated the specific requirements for the GmRIN4 proteins in R-mediated resistance and examined the mechanism of Rpg1-b activation.
  • Using virus-induced gene silencing, we show that only GmRIN4a and b are required for Rpg1-b-mediated resistance. In planta binding assays show that GmRIN4a can associate with Rpg1-b indirectly via GmRIN4b. Pathogen-delivered AvrB induces the phosphorylation of GmRIN4b alone, and prevents interactions between GmRIN4b and Rpg1-b or GmRIN4a.
  • Consistent with this result, a phosphomimic derivative of GmRIN4b (pm4b) fails to bind Rpg1-b and GmRIN4a. Conversely, a phosphodeficient derivative of GmRIN4b (pd4b) continues to bind the R protein and GmRIN4a, in the presence of AvrB. Coexpression of Rpg1-b with pm4b, but not GmRIN4b or pd4b, induces cell death and ion leakage in the heterologous Nicotiana benthamiana.
  • Our data suggest that the AvrB-induced phosphorylation of GmRIN4b, and the subsequent inhibition of interaction among GmRIN4b, GmRIN4a and Rpg1-b, might activate the R protein. Furthermore, even though GmRIN4c and d are not required for Rpg1-b-derived resistance, they do function in resistance derived from other R loci.