More stories to tell: NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1, a salicylic acid receptor.

Salicylic acid (SA) plays pivotal role in plant defense against biotrophic and hemibiotrophic pathogens. Tremendous progress has been made in the field of SA biosynthesis and SA signaling pathways over the past three decades. Among the key immune players in SA signaling pathway, NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1) functions as a master regulator of SA-mediated plant defense. The function of NPR1 as an SA receptor has been controversial; however, after years of arguments among several laboratories, NPR1 has finally been proven as one of the SA receptors. The function of NPR1 is strictly regulated via post-translational modifications and transcriptional regulation that were recently found. More recent advances in NPR1 biology, including novel functions of NPR1 and the structure of SA receptor proteins, have brought this field forward immensely. Therefore, based on these recent discoveries, this review acts to provide a full picture of how NPR1 functions in plant immunity and how NPR1 gene and NPR1 protein are regulated at multiple levels. Finally, we also discuss potential challenges in future studies of SA signaling pathway.