Identification of the maize Mediator CDK8 module, and Dissociation insertional mutagenesis of ZmMed12a

Mediator is a conserved transcriptional co-activator that links transcription factors bound at enhancer elements to RNA Polymerase II. Mediator-RNA Polymerase II interactions can be sterically hindered by the Cyclin Dependent Kinase 8 (CDK8) module, a submodule of Mediator that acts to repress transcription in response to discrete cellular and environmental cues. The CDK8 module is conserved in all eukaryotes and consists of 4 proteins: CDK8, CYCLIN C (CYCC), MED12, and MED13. In this study, we have characterized the CDK8 module of Mediator in maize. The maize genome contains single copy genes for Cdk8, CycC, and Med13, and two genes for Med12. Analysis of expression data for the CDK8 module demonstrated that all five genes are broadly expressed in maize tissues, with ZmMed12a, ZmMed12b, and ZmMed13 exhibiting similar expression patterns. We performed a Dissociation (Ds) insertional mutagenesis, recovering two independent insertions in the ZmMed12a gene. One of these Ds insertions results in a truncation of the ZmMed12a transcript. Our molecular characterization of the maize CDK8 module, as well as transposon tagging of ZmMed12a, establish the basis for molecular and functional studies of these important transcriptional regulators in Zea mays.