Posttranslational Modifications of NPR1: Dynamic Regulation of Immune Responses through the Interplay of Sumoylation and Phosphorylation
J. WITHERS (1) (1) Duke University, U.S.A.

NPR1 is a master regulator of salicylic acid (SA)-mediated basal and systemic acquired resistance in plants. NPR1 translocation into the nucleus is required for 99% of the transcriptomic changes triggered by SA, but how this single protein orchestrates genome-wide transcriptional reprogramming remains a major question. Since NPR1 transcription is not dramatically affected by pathogen challenge, studies of NPR1 have been focused on protein interactors and post translational modifications (PTMs). In response to increases in cellular SA levels, NPR1 activity and degradation are dynamically regulated by the interplay between sumoylation and phosphorylation. Sumoylation of NPR1 is required for phosphorylation at Ser11/Ser15 and switches its association from WRKY to TGA transcription factors, which repress and activate defense genes, respectively. In the absence of SA accumulation, sumoylation of NPR1 is inhibited through phosphorylation at Ser55/Ser59, keeping NPR1 stable and quiescent. Through phosphoproteomic analyses, we have identified a novel phosphorylation site in NPR1. While this phosphorylation event does not affect interactions with previously characterized NPR1 protein partners, it dramatically affects NPR1-dependent defense gene expression. Our results indicate that this PTM may be functioning to regulate the transcriptional activity of NPR1 at defense gene promoters.

Abstract Number: P16-479
Session Type: Poster