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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 using genomic, molecular and functional resources. 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, and change their expression in response to phosphate and nitrogen limitation. We performed Dissociation (Ds) insertional mutagenesis, recovering two independent insertions in the ZmMed12a gene, one of which produces a truncated transcript. Our molecular identification of the maize CDK8 module, assays of CDK8 module expression under nutrient limitation, and characterization of transposon insertions in ZmMed12a establish the basis for molecular and functional studies of the role of these important transcriptional regulators in development and nutrient homeostasis in Zea mays.

Plant PHO1 proteins play a central role in the translocation and sensing of inorganic phosphate. The maize (

PHO1 proteins play a central role in plant inorganic phosphorus translocation and sensing. The maize (Zea mays ssp. mays) genome encodes two co-orthologs of the Arabidopsis PHO1 gene, designated ZmPho1;2a and ZmPho1;2b. Here, we report the characterization of the transposon-footprint allele Zmpho1;2a’-m1.1, which we refer to hereafter as pho1;2a. The pho1;2a allele is a stable derivative formed by excision of an Activator element from the ZmPho1;2a gene. The pho1;2a allele contains an 8 bp insertion at the point of excision that disrupts the reading frame and is predicted to generate a premature translational stop. We show that the pho1;2a allele is linked to a dosage-dependent reduction in transcript accumulation and a mild reduction in seedling growth that is enhanced under nutrient deficient conditions. Characterization of the shoot and root transcriptomes of seedlings segregating the pho1;2a mutation under different nutrient conditions revealed pho1;2a to have a dominant effect on patterns of transcript accumulation. Gene set enrichment analysis of the transcripts mis-regulated in pho1;2a mutants suggests that Pho1;2a functions in the fine-tuning of the transcriptional phosphate starvation response. We discuss our results with reference to possible genetic redundancy among maize Pho1 genes and in the context of reports linking functional variation in Pho1;2a to agronomically important traits.

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 forCdk8, CycC,andMed13,and two genes forMed12.Analysis of expression data for the CDK8 module demonstrated that all five genes are broadly expressed in maize tissues, withZmMed12a, ZmMed12b,andZmMed13exhibiting similar expression patterns. We performed aDissociation (Ds)insertional mutagenesis, recovering two independent insertions in theZmMed12agene. One of theseDsinsertions results in a truncation of theZmMed12atranscript. Our molecular characterization of the maize CDK8 module, as well as transposon tagging ofZmMed12a,establish the basis for molecular and functional studies of these important transcriptional regulators inZea mays.