Internal medicine

Receptor

Transcriptional regulation

Heart failure

Salicylic acid

Transcription factor

Biology

Activator (genetics)

Gene

Function (biology)

Repressor

Natriuretic peptide

Immunity

Cell biology

Genetics

Biochemistry

Medicine

NPR1

Immune system

Cell

Salicylic acid (SA) is a plant defense hormone required for immunity. Arabidopsis NPR1 and NPR3/NPR4 were previously shown to bind SA and all three proteins were proposed as SA receptors. NPR1 functions as a transcriptional co-activator, whereas NPR3/NPR4 were suggested to function as E3 ligases that promote NPR1 degradation. Here we report that NPR3/NPR4 function as transcriptional co-repressors and SA inhibits their activities to promote the expression of downstream immune regulators. npr4-4D, a gain-of-function npr4 allele that renders NPR4 unable to bind SA, constitutively represses SA-induced immune responses. In contrast, the equivalent mutation in NPR1 abolishes its ability to bind SA and promote SA-induced defense gene expression. Further analysis revealed that NPR3/NPR4 and NPR1 function independently to regulate SA-induced immune responses. Our study indicates that both NPR1 and NPR3/NPR4 are bona fide SA receptors, but play opposite roles in transcriptional regulation of SA-induced defense gene expression.

Opposite Roles of Salicylic Acid Receptors NPR1 and NPR3/NPR4 in Transcriptional Regulation of Plant Immunity