| Popis: |
In plants and animals, cell identity is maintained by epigenetic functions that prevent changes in cell type specific transcription programs, for example, in the control of homeotic gene expression patterns that specify regional fate during development. Central to the cell memory machinery are the Polycomb-Group (Pc-G) genes. The Arabidopsis (Pc-G) genes FERTILISATION-INDEPENDENT ENDOSPERM (FIE), FERTILISATION INDEPENDENT SEED 2 (FIS2) and MEDEA (MEA) are required for ovule and seed development. These three genes confer similar mutant phenotypes in both unfertilized embryo sacs and developing seeds; that is, fertilisation-independent endosperm proliferation and the abortion of fertilised seeds that carry a maternally inherited mutant mea, fis2 or fie allele. I have shown that MEA and FIE, and MEA and FIS2 interact in yeast-two-hybrid, and that the interaction of MEA and FIE is mediated by the amino-terminal region of MEA, whilst interaction of MEA and FIS2 requires the FIS2 C-terminal VEFS box. Furthermore, FIE and MEA RNA expression over-laps in vivo and the proteins co-localise within the nucleus in planta. I conclude that the similarity of the fie, fis2, and mea phenotypes reflects the interaction of their gene products as part of a multiprotein complex. FIE, MEA and FIS2 do not possess specific DNA binding activity, and it remains unclear how the FIE complex is directed to its target genes. Yeast-two-hybrid assays were used to identify a novel FIE interacting protein: RAP-1, a member of the basic helix loop helix (bHLH) family of transcription factors. Molecular and genetic studies were used to characterise its interaction with FIE. FIE is expressed in both embryo and endosperm, but predominantly affects endosperm development. In order to establish if FIE is needed in both, I have used a strategy for targeted expression of FIE to the embryo and endosperm regions in a fie background, and observed a partial rescue of fie. |
