Suppression of MYC transcription activators by the immune cofactor NPR1 fine-tunes plant immune responses (Cell Reports)

In Arabidopsis, NONEXPRESSOR OF PR GENES 1 (NPR1) plays an important role in the antagonistic crosstalk of salicylic acid (SA) and jasmonic acid (JA) signalling. It activates SA-induced genes that protect against biotrophic pathogens and suppresses JA-induced genes that protect against necrotrophic pathogens. The biotrophic Pseudomonas syringae pv. tomato overcomes the plant’s SA-induced immune response by producing the toxin coronatine (COR), which mimics biologically active JA that suppresses SA-induced immunity. Here, Nomoto et al. show the molecular mechanism whereby SA-induced NPR1 in turn negatively regulates JA-responsive genes. Through in vitro and in vivo experiments, the authors demonstrate that NPR1 interacts with the transcription factor MYC2, preventing it from associating with the MED25 subunit of the Mediator transcriptional co-activator complex and performing its role as a transcriptional activator of JA-induced genes. RNAseq and ChIP-seq experiments reveal that NPR1 targets JA-responsive promoters, co-occupied by transcriptionally active MYC2-MED25 complexes. ChIP experiments also show how SA-signalling does not prevent MYC2 binding to JA-responsive promoters but does prevent MED25 accumulation. Using Pseudomonas syringae pathogen assays, the authors demonstrate how NPR1 suppresses MYC activators to overcome COR-mediated infection. (Summary by Jiawen Chen @Jiaaawen) Cell Reports 10.1016/j.celrep.2021.110125