Component of the Mediator complex, a coactivator involved in the regulated transcription of nearly all RNA polymerase II-dependent genes. Mediator functions as a bridge to convey information from gene-specific regulatory proteins to the basal RNA polymerase II transcription machinery. The Mediator complex, having a compact conformation in its free form, is recruited to promoters by direct interactions with regulatory proteins and serves for the assembly of a functional pre-initiation complex with RNA polymerase II and the general transcription factors (PubMed:22021418, PubMed:24451981). Involved in the regulation of histone H3 lysine tri-methylation (H3K36me3). Associates with the promoter, coding and terminator regions of target genes suggesting its function in transcription initiation, elongation and termination. Multifunctional protein which regulates plant immunity, especially during necrotrophic fungal infection (e.g. B.cinerea and A.brassicicola), flowering time and responses to hormones (e.g. abscisic acid ABA and ethylene) through interactions with distinct transcription factors (PubMed:24451981). Component of the Mediator complex (PubMed:17560376). Interacts with YY1 to suppress disease susceptibility via the repression of genes glutaredoxins GRX480, GRXS13 and thioredoxin TRX-h5. Binds to ABI4 to regulate abscisic acid responses; recruited by ABI4 to ABI5 promoter in the presence of abscisic acid (ABA). Interacts with SUF4 to regulate flowering time; recruited by SUF4 to FLC promoter (PubMed:24451981). Deregulated expression of glutaredoxins GRX480, GRXS13 and thioredoxin TRX-h5 leading to enhanced susceptibility to fungal infection (e.g. B.cinerea and A.brassicicola). Altered RNA polymerase II occupancy and histone H3 lysine tri-methylation (H3K36me3) of target genes. Insensitivity to abscisic acid (ABA) and to the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). Delayed flowering. Belongs to the Mediator complex subunit 18 family.