https://www.cell.com/cell/pdf/S0092-8674(02)00807-3.pdf

DEMETER, a DNA Glycosylase Domain Protein, Is Required for Endosperm Gene Imprinting and Seed Viability in Arabidopsis

Role of the Arabidopsis DRM Methyltransferases in De Novo DNA Methylation and Gene Silencing

http://fischerlab.berkeley.edu/sites/default/files/fischerlab/Gehring_2006.pdf

DEMETER DNA Glycosylase Establishes MEDEA Polycomb Gene Self-Imprinting by Allele-Specific Demethylation

We report here the isolation of the Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1 (AtSERK1) gene and we demonstrate its role during establishment of somatic embryogenesis in culture. The AtSERK1 gene is highly expressed during embryogenic cell formation in culture and during early embryogenesis. The AtSERK1 gene is first expressed in planta during megasporogenesis in the nucleus of developing ovules, in the functional megaspore, and in all cells of the embryo sac up to fertilization. After fertilization, AtSERK1 expression is seen in all cells of the developing embryo until the heart stage. After this stage, AtSERK1 expression is no longer detectable in the embryo or in any part of the developing seed. Low expression is detected in adult vascular tissue. Ectopic expression of the full-length AtSERK1 cDNA under the control of the cauliflower mosaic virus 35S promoter did not result in any altered plant phenotype. However, seedlings that overexpressed the AtSERK1 mRNA exhibited a 3- to 4-fold increase in efficiency for initiation of somatic embryogenesis. Thus, an increased AtSERK1 level is sufficient to confer embryogenic competence in culture.

http://smcg.ccg.unam.mx/actividades/pre_congresos/SMB_Vallarta2002/Vielle/Hecht2001.pdf

The Arabidopsis Somatic Embryogenesis Receptor Kinase 1 Gene Is Expressed in Developing Ovules and Embryos and Enhances Embryogenic Competence in Culture

The Arabidopsis FWA gene was initially identified from late-flowering epigenetic mutants that show ectopic FWA expression associated with heritable hypomethylation of repeats around transcription starting sites. Here, we show that wild-type FWA displays imprinted (maternal origin-specific) expression in endosperm. The FWA imprint depends on the maintenance DNA methyltransferase MET1, as is the case in mammals. Unlike mammals, however, the FWA imprint is not established by allele-specific de novo methylation. It is established by maternal gametophyte-specific gene activation, which depends on a DNA glycosylase gene, DEMETER. Because endosperm does not contribute to the next generation, the activated FWA gene need not be silenced again. Double fertilization enables plants to use such "one-way" control of imprinting and DNA methylation in endosperm.

https://science.sciencemag.org/content/sci/303/5657/521.full.pdf

One-way control of FWA imprinting in Arabidopsis endosperm by DNA methylation.

In higher plants, seed development requires maternal gene activity in the haploid (gametophytic) as well as diploid (sporophytic) tissues of the developing ovule. The Arabidopsis thaliana gene MEDEA (MEA) encodes a SET-domain protein of the Polycomb group that regulates cell proliferation by exerting a gametophytic maternal control during seed development. Seeds derived from female gametocytes (embryo sacs) carrying a mutant mea allele abort and exhibit cell proliferation defects in both the embryo and the endosperm. In this study we show that the mea mutation affects an imprinted gene expressed maternally in cells of the female gametophyte and after fertilization only from maternally inherited MEA alleles. Paternally inherited MEA alleles are transcriptionally silent in both the young embryo and endosperm. Mutations at the decrease in DNA methylation1 (ddm1) locus are able to rescue mea seeds by functionally reactivating paternally inherited MEA alleles during seed development. Rescued seeds are larger than the wild type and exhibit some of the abnormalities found in aborting mea seeds. Our results indicate that the maintenance of the genomic imprint at the mea locus requires zygotic DDM1 activity. Because DDM1 encodes a putative chromatin remodeling factor, chromatin structure is likely to be interrelated with genomic imprinting in Arabidopsis.

/pdf/maintenance-of-genomic-imprinting-at-the-arabidopsis-medea-34bxkhtpxy.pdf

Julie Thomas

Papers

Maintenance of genomic imprinting at the Arabidopsis medea locus requires zygotic DDM1 activity