Mechanisms of gene repression by vernalization in Arabidopsis.

FLOWERING LOCUS C (FLC) is a major regulator of flowering time in Arabidopsis. Repression of FLC occurs in response to prolonged cold exposure (vernalization) and is associated with an enrichment of the repressive histone modification trimethylated H3 lysine 27 (H3K27me3) and a depletion of the active histone modification H3K4me3 at FLC chromatin. In two cases genes adjacent to FLC are also repressed by vernalization.

Resetting of FLOWERING LOCUS C expression after epigenetic repression by vernalization.

The epigenetic repression of FLOWERING LOCUS C (FLC) in winter-annual ecotypes of Arabidopsis by prolonged cold ensures that plants flower in spring and not during winter. Resetting of the FLC expression level in progeny is an important step in the life cycle of the plant. We show that both the paternally derived and the maternally derived FLC:GUS genes are reset to activity but that the timing of their first expression differs.

Reciprocal control of flowering time by OsSOC1 in transgenic Arabidopsis and by FLC in transgenic rice.

In a screen for MADS box genes which activate and/or repress flowering in rice, we identified a gene encoding a MADS domain protein (OsSOC1) related to the Arabidopsis gene AtSOC1. AtSOC1 and OsSOC1 show a 97% amino acid similarity in their MADS domain. The rice gene contains a large first intron of 27.

Quantitative effects of vernalization on FLC and SOC1 expression.

Prolonged exposure to cold results in early flowering in Arabidopsis winter annual ecotypes, with longer exposures resulting in a greater promotion of flowering than shorter exposures. The promotion of flowering is mediated through an epigenetic down-regulation of the floral repressor FLOWERING LOCUS C (FLC). We present results that provide an insight into the quantitative regulation of FLC by vernalization.

The downregulation of FLOWERING LOCUS C (FLC) expression in plants with low levels of DNA methylation and by vernalization occurs by distinct mechanisms.

FLOWERING LOCUS C (FLC), a repressor of flowering, is a major determinant of flowering time in Arabidopsis. FLC expression is repressed by vernalization and in plants with low levels of DNA methylation, resulting in early flowering. This repression is not associated with changes of DNA methylation within the FLC locus in either vernalized plants or plants with low levels of DNA methylation.

A cluster of Arabidopsis genes with a coordinate response to an environmental stimulus.

Vernalization, the promotion of flowering after prolonged exposure to low temperatures, is an adaptive response of plants ensuring that flowering occurs at a propitious time in the annual seasonal cycle. In Arabidopsis, FLOWERING LOCUS C (FLC), which encodes a repressor of flowering, is a key gene in the vernalization response; plants with high-FLC expression respond to vernalization by downregulating FLC and thereby flowering at an earlier time. Vernalization has the hallmarks of an epigenetically regulated process.

Different regulatory regions are required for the vernalization-induced repression of FLOWERING LOCUS C and for the epigenetic maintenance of repression.

Vernalization, the promotion of flowering by a prolonged period of low temperature, results in repression of the floral repressor FLOWERING LOCUS C (FLC) and in early flowering. This repression bears the hallmark of an epigenetic event: the low expression state is maintained over many cell division cycles, but expression is derepressed in progeny. We show that the two stages of the response of FLC to vernalization, the repression of FLC and the maintenance of the repression during growth at normal temperatures after vernalization, are mediated through different regions of the FLC gene.

FLC, a repressor of flowering, is regulated by genes in different inductive pathways.

The MADS-box protein encoded by FLOWERING LOCUS C (FLC) is a repressor of flowering. Loci in the autonomous flowering pathway control FLC levels. We show the epistatic groupings of autonomous pathway mutants fca/fy and fve/fpa, based on their effects on flowering time, are consistent with their effects on FLC transcript and protein levels.