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

Transposons and tandem repeats are not involved in the control of genomic imprinting at the MEDEA locus in Arabidopsis.

MEDEA Takes Control of Its Own Imprinting

Genomic imprinting is an essential epigenetic process that controls the size of seeds in flowering plants. In Arabidopsis, DEMETER activates the maternal copy of the imprinted MEDEA Polycomb gene. In this issue of Cell, Gehring et al. (2006) demonstrate that this activation involves DNA demethylation of MEDEA by DEMETER. Remarkably, they also find that silencing of the paternal MEDEA allele is ...

Maintenance of DNA methylation during the Arabidopsis life cycle is essential for parental imprinting.

Imprinted genes are expressed predominantly from either their paternal or their maternal allele. To date, all imprinted genes identified in plants are expressed in the endosperm. In Arabidopsis thaliana, maternal imprinting has been clearly demonstrated for the Polycomb group gene MEDEA (MEA) and for FWA. Direct repeats upstream of FWA are subject to DNA methylation. However, it is still not cl...

Characterization of an Arabidopsis thaliana DNA hypomethylation mutant

We have recently isolated two Arabidopsis thaliana DNA hypomethylation mutations, identifying the DDM1 locus, that cause a 70% reduction in genomic 5-methylcytosine levels [1]. Here we describe further phenotypic and biochemical characterization of the ddm1 mutants. ddm1/ddm1 homozygotes exhibited altered leaf shape, increased cauline leaf number, and a delay in the onset of flowering when comp...

Plant development:: Medea's maternal instinct

The Arabidopsis MEDEA gene is required in maternal tissues to restrict cell proliferation in embryos. Molecular characterisation indicates that MEDEA encodes a Polycomb-group protein, particularly intriguing as MEDEA's maternal effects may be a consequence of genomic imprinting.