How members of the NPR receptor family sense the SAR signal salicylic acid – the alternate model 
U. PFITZNER (1), D. Neeley (1), F. Maier (1), E. Konopka (1) (1) Universitaet Hohenheim, Germany

Salicylic acid (SA) is an endogenous hormone mediating diverse processes in plants including pathogen defense during systemic acquired resistance (SAR). Genetic evidence has established unambigously that NONEXPRESSOR OF PR GENES1 (NPR1/NIM1) is the central regulator of SAR. NPR1 transmits the SAR signal SA to induce expression of PR genes. In Arabidopsis, NPR1 is part of a gene family encompassing six members. Biochemical analyses predicted that four members, NPR1 to NPR4, are able to sense SA. Indeed, binding of SA has been reported recently for NPR3 and NPR4 and for NPR1. However, an open controversy has arisen about the identity of the SA receptor in SAR and the mechanism of SA perception. We propose an alternate model for SA perception through NPR1. Using yeast as a system for biochemical dissection of NPR proteins, we demonstrate that binding of SA engages two highly conserved domains in the C-terminal regions of NPR family members, the LENRV motif and the binding domain for NIM1-INTERACTING (NIMIN) proteins. Our model implies that NPR proteins undergo conformational remodeling upon SA perception, concomitant with gain of transcription activity. Of note, SA is sensed differentially by NPR family members. Our conclusions are corroborated by numerous NPR1 mutants identified in independent genetic screens in Arabidopsis. Furthermore, our data provide a biochemical basis for regulatory activity of SA-induced NIMIN proteins in PR-1 gene expression.

Abstract Number: P16-466
Session Type: Poster