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 preinitiation complex with RNA polymerase II and the general transcription factors. Regulator of both plant defense and flowering time. Involved in pollen tube growth. Component of the Mediator complex. Increased number of leaves and shorter petioles under vegetative conditions. Late-flowering phenotype when grown under both long-day and short-day conditions. Increased sensitivity to necrotrophic pathogens. Named seth after the brother and murderer of the Egyptian fertility god Osiris. Belongs to the Mediator complex subunit 8 family.