CYCLIN-DEPENDENT KINASE8 Differentially Regulates Plant Immunity to Fungal Pathogens through Kinase-Dependent and -Independent Functions in Arabidopsis    

Abstract

CYCLIN-DEPENDENT KINASE8 (CDK8) is a widely studied component of eukaryotic Mediator complexes. However, the biological and molecular functions of plant CDK8 are not well understood. Here, we provide evidence for regulatory functions of Arabidopsis thaliana CDK8 in defense and demonstrate its functional and molecular interactions with other Mediator and non-Mediator subunits. The cdk8 mutant exhibits enhanced resistance to Botrytis cinerea but susceptibility to Alternaria brassicicola. The contributions of CDK8 to the transcriptional activation of defensin gene PDF1.2 and its interaction with MEDIATOR COMPLEX SUBUNIT25 (MED25) implicate CDK8 in jasmonate-mediated defense. Moreover, CDK8 associates with the promoter of AGMATINE COUMAROYLTRANSFERASE to promote its transcription and regulate the biosynthesis of the defense-active secondary metabolites hydroxycinnamic acid amides. CDK8 also interacts with the transcription factor WAX INDUCER1, implying its additional role in cuticle development. In addition, overlapping functions of CDK8 with MED12 and MED13 and interactions between CDK8 and C-type cyclins suggest the conserved configuration of the plant Mediator kinase module. In summary, while CDK8's positive transcriptional regulation of target genes and its phosphorylation activities underpin its defense functions, the impaired defense responses in the mutant are masked by its altered cuticle, resulting in specific resistance to B. cinerea.

The Arabidopsis Mediator Complex Subunit16 Is a Key Component of Basal Resistance against the Necrotrophic Fungal Pathogen Sclerotinia sclerotiorum

“…1). Although med8, med13, and med18 have been shown to be more susceptible than the wild type to the necrotrophic fungal pathogens B. cinerea and A. brassicicola (Kidd et al, 2009;Lai et al, 2014;Zhu et al, 2014), they did not show enhanced susceptibility to S. sclerotiorum. This is probably because MED8, MED13, and MED18 do not play a major role in regulating S. sclerotiorum-induced transcriptome changes (Fig.…”

“…MED14, MED15, MED16, and MED19a have been shown to regulate the SA-triggered immunity against biotrophic and hemibiotrophic pathogens (Canet et al, 2012;Zhang et al, 2012Zhang et al, , 2013Caillaud et al, 2013), whereas MED8, MED12, MED13, MED16, MED21, MED25, and CDK8 have been found to function in JA/ET-mediated immunity against necrotrophic pathogens (Dhawan et al, 2009;Kidd et al, 2009;Zhang et al, 2012;Zhu et al, 2014). MED18 also functions in resistance to necrotrophic pathogens, but the resistance is independent of the JA/ET signaling (Lai et al, 2014).…”

Transcriptional Regulation of Pattern-Triggered Immunity in Plants

“…MED14, MED15 and MED16 contribute to SA-mediated plant local and systemic resistance to Pst (Zhang et al, 2013). CDK8, MED12 and MED13, the kinase module of the Mediator complex, also play important roles in plant immunity to necrotrophic fungi and Pst (Zhu et al, 2014). Systematic characterization of various PTI outputs triggered by purified MAMPs or Pst hrcC in individual Mediator complex mutants can help reveal whether and how Mediator directly conveys PRR signaling to selective activation of MAMP-responsive genes.…”

“…Notably, ERF1 and ORA59 regulate different JA-responsive genes from those regulated by MYC2 (Cevik et al, 2012). In addition, MED25 as well as its interacting subunit CDK8 also regulate the expression of ERF1 and ORA59 by binding to their promoters (Cevik et al, 2012; Zhu et al, 2014). Moreover, MED16 directly interacts with WRKY33, a member of the WRKY family of plant-specific transcription factors (discussed below in detail) and is essential for the recruitment of RNAPII to the WRKY33 target genes PDF1.2 and ORA59, suggesting a specific role of MED16 in mediating the transcriptional regulation of WRKY33 target genes (Wang et al, 2015).…”

Arabidopsis HOOKLESS1 regulates responses to pathogens and abscisic acid through interaction with MED18 and acetylation of WRKY33 and ABI5 chromatin

“…The co-IP was conducted following the previously described procedure (Lai et al, 2014;Zhu et al, 2014). Briefly, the plasmids containing full-length HLS1-HA and MED18-MYC driven by the CaMV 35S promoter were generated and transformed into Agrobacterium.…”