The CYCLIN-DEPENDENT KINASE Module of the Mediator Complex Promotes Flowering and Reproductive Development in Pea(1)([OPEN])

Control of flowering time has been a major focus of comparative genetic analyses in plant development. This study reports on a forward genetic approach to define previously uncharacterized components of flowering control pathways in the long-day legume, pea (Pisum sativum). We isolated two complementation groups of late-flowering mutants in pea that define two uncharacterized loci, LATE BLOOMER3 (LATE3) and LATE4, and describe their diverse effects on vegetative and reproductive development. A map-based comparative approach was employed to identify the underlying genes for both loci, revealing that that LATE3 and LATE4 are orthologs of CYCLIN DEPENDENT KINASE8 (CDK8) and CYCLIN C1 (CYCC1), components of the CDK8 kinase module of the Mediator complex, which is a deeply conserved regulator of transcription in eukaryotes. We confirm the genetic and physical interaction of LATE3 and LATE4 and show that they contribute to the transcriptional regulation of key flowering genes, including the induction of the florigen gene FTa1 and repression of the floral repressor LF. Our results establish the conserved importance of the CDK8 module in plants and provide evidence for the function of CYCLIN C1 orthologs in the promotion of flowering and the maintenance of normal reproductive development. Characterization of two loci influencing flowering initiation and reproductive development, LATE3 and LATE4, reveals an important role for the deeply conserved Mediator complex.