Mediator Subunit, Med14, Regulates Pre- and Post-Fertilization Developmental Events in <i>Arabidopsis</i>

Abstract

In flowering plants, transitions from vegetative-to-reproductive and reproductive-to-seed stages are tightly regulated by coordinated activity of multiple transcription factors and cofactors. However, the mechanism of communication and coordination between these transcription regulators during ovule and seed development is not fully understood. This study reveals that the Mediator subunit MED14 integrates transcriptional signals from different transcription factors during pre-and post-fertilization developmental events in Arabidopsis. This is also the first study to demonstrate the importance of parental contribution of any Mediator subunit. We found that the promoter of AtMED14 is active in the auxin maxima regions of meristematic zones. We were unable to obtain any homozygous line of MED14 knock-out. The heterozygous mutants of med14 show defects in embryo sac, fertilization, and seed development. The genetic and cytological analyses revealed that the defective maternal sporophytic reproductive part of the med14+/- mutant is responsible for the fertilization defects. Some of the med14 embryos are arrested at globular stage whereas few others have uncontrolled cell division forming globular mass of cells. The auxin signaling essential for the ovule, embryo and seed development is compromised in med14 mutants. Further, MED14 is also important for seed coat development and its mucilage content as it interacts with different transcription regulators like ANT, WUS, LUG, MYB5, KNAT7 and LUH to regulate the expression of enzymes like MUM2 and MUM4 that are required for the synthesis of seed mucilage and its release, respectively. Overall, this study establishes MED14 as an important convergence point of transcriptional signals from various transcription factors required for development of gynoecium and seed in Arabidopsis.