Abstract
DNA demethylation is involved in many developmental and differentiative processes of plants and animals. In flowering plants, genomic imprinting is established by DNA demethylation in the central cell. DEMETER (DME) DNA glycosylase excises 5-methylcytosine and activates the maternal imprinted genes including FWA. This epigenetic reprogramming is controlled via base-excision repair machinery and is inherited to the endosperm. However, other processes rather than removal of 5-methylcytosine remain unknown. To understand the regulatory mechanism of DNA demethylation, we screened the mutants that are defective in FWA expression using FWA-GFP reporter plants.
We isolated alac1 mutant encoding histone chaperone. Although alac1 did not affect DME expression in the central cell, alac1 was defective in DNA demethylation and activation of maternal imprinted genes. alac1 also exhibits endosperm over-proliferation and autonomous endosperm development without fertilization, which is similar to the mutants of imprinted genes. These results indicate ALAC1 histone chaperone gene is involved in the establishment of genomic imprinting through DNA demethylation.
