Figure 8.

Schematic model of the roles of NPR1 and CDK8 in the transcriptional regulation of NPR1 and PR1 genes. Left, Activation of NPR1 gene expression by NPR1 and CDK8. Pathogen infection induces the expression of the CDK8 gene. CDK8 interacts with the WRKY6 and WRKY18 TFs, which bind to the NPR1 gene promoter at the W-box motif. SA promotes the interactions between NPR1 and CDK8 and between NPR1 and WRKY18. CDK8 and other proteins in the kinase module of the Mediator complex, including MED12 and MED13, bring RNA polymerase II (Pol II) to the NPR1 gene promoter and coding region to promote its transcription. NPR1 mRNA is then exported to the cytosol for NPR1 protein synthesis. Right, CDK8 facilitates the expression of the PR1 gene. After CDK8 and NPR1 induce the transcription of the NPR1 gene, NPR1 protein is synthesized and reduced from oligomers to monomers upon pathogen infection, then NPR1 monomers enter the nucleus. In the nucleus, NPR1 forms a protein complex with CDK8, TGA5, and TGA7, which bind to the PR1 promoter at the as-1 sequence. RNA polymerase II is then recruited to the promoter and coding region of the PR1 gene by CDK8, MED12, and MED13 to facilitate PR1 gene expression to activate plant defense.