Highlights•Salicylic acid (SA) is a plant defense hormone with critical roles in PTI, ETI and
SAR.•Induction of SA synthesis is orchestrated via complex transcriptional regulation of
ICS1.•SA is perceived by two types of receptors, NPR1 and NPR3/NPR4.•SA-binding
activates NPR1 to promote expression of downstream defence genes.•SA-binding inhibits
NPR3/NPR4, leading to de-repression of SA-responsive genes.Salicylic acid (SA) has
emerged as a key plant defense hormone with critical roles in different aspects of plant …

Salicylic acid (SA) has emerged as a key plant defense hormone with critical roles in
different aspects of plant immunity. Analysis of Arabidopsis mutants revealed complex
regulation of pathogen-induced SA biosynthesis. Studies on SA-insensitive mutants led to
the identification of the SA receptors and how SA regulates defense gene expression.
Consistent with its critical roles in plant immunity, SA is required for the assembly of a normal
root microbiome and various pathogen effectors have evolved to target components of SA …