Differential roles of NPR proteins in regulating SA signalling (Cell) ($)

Salicylic acid is a small phenolic hormone that plays a prominent role in the regulation of plant immune responses. Exactly how SA is perceived in planta has been an intensive area of research, with differential paradigms proposed for the perception of SA through negative regulators NPR3/NPR4 or through the master regulator NPR1. In a new study published in Cell, Ding et al. (2018) identified an npr4 mutant allele producing a dominant negative protein that no longer binds SA and is therefore a constitutive repressor of SA signalling. Importantly, the authors demonstrate that rather than acting as a regulator of NPR1 protein stability, NPR4/NPR3 function as co-transcriptional repressors that regulate SA signalling independent of NPR1. Collectively, the data provide an updated model for the perception of SA through the contrasting roles of SA-binding NPR proteins. (Summary by Philip Carella) Cell 10.1016/j.cell.2018.03.044