title: DNA methylation, vernalization, and the initiation of flowering.
abstract: Late-flowering ecotypes and mutants of Arabidopsis thaliana and the related crucifer Thlaspi arvense flower early after cold treatment (vernalization). Treatment with the DNA demethylating agent 5-azacytidine induced nonvernalized plants to flower significantly earlier than untreated controls. Cytidine at similar concentrations had no effect on time to flower. In contrast, late-flowering mutants that are insensitive to vernalization did not respond to 5-azacytidine treatment. Normal flowering time was reset in the progeny of plants induced to flower early with 5-azacytidine, paralleling the lack of inheritance of the vernalized condition. Arabidopsis plants, either cold-treated or 5-azacytidine-treated, had reduced levels of 5-methylcytosine in their DNA compared to nonvernalized plants. A Nicotiana plumbaginifolia cell line also showed a marked decrease in the level of 5-methylcytosine after treatment with either 5-azacytidine or low temperature. We suggest that DNA methylation provides a developmental control preventing early flowering in Arabidopsis and Thlaspi ecotypes. Vernalization, through its general demethylating effect, releases the block to flowering initiation. We propose that demethylation of a gene critical for flowering permits its transcription. We further suggest, on the basis of Thlaspi data, that the control affects transcription of kaurenoic acid hydroxylase, a key enzyme in the gibberellic acid biosynthetic pathway.
authors.affiliation: Division of Plant Industry, Commonwealth Scientific and Industrial Research Organization, Canberra, Australia.
authors.forename: J E
authors.initials: JE
authors.lastname: Burn
authors.forename: D J
authors.initials: DJ
authors.lastname: Bagnall
authors.forename: J D
authors.initials: JD
authors.lastname: Metzger
authors.forename: E S
authors.initials: ES
authors.lastname: Dennis
authors.forename: W J
authors.initials: WJ
authors.lastname: Peacock