The Plant cellOct 27, 2009

ARABIDOPSIS TRITHORAX-RELATED7 is needed to add a chemical mark that turns on the flowering gene FLOWERING LOCUS C

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Mar 29, 2026

Abstract

The atxr7 mutation in Arabidopsis thaliana reduces FLC expression and promotes rapid flowering.

An active allele of FRIGIDA (FRI) increases the expression of FLOWERING LOCUS C (FLC), which delays flowering.
The putative H3K4 methylase ARABIDOPSIS TRITHORAX-RELATED7 (ATXR7) is necessary for maintaining appropriate FLC levels.
The atxr7 mutation leads to lower FLC expression and alters histone modifications, specifically decreasing H3K4 methylation and increasing H3K27 methylation.
Both ATXR7 and another H3K4 methylase, encoded by ATX1, are needed for proper regulation of FLC expression, as shown by the additive flowering phenotype in atx1 atxr7 double mutants.

Simplified

In the winter-annual accessions of Arabidopsis thaliana, presence of an active allele of FRIGIDA (FRI) elevates expression of FLOWERING LOCUS C (FLC), a repressor of flowering, and thus confers a vernalization requirement. FLC activation by FRI involves methylation of Lys 4 of histone H3 (H3K4) at FLC chromatin. Many multicellular organisms that have been examined contain two classes of H3K4 methylases, a yeast (Saccharomyces cerevisiae) Set1 class and a class related to Drosophila melanogaster Trithorax. In this work, we demonstrate that ARABIDOPSIS TRITHORAX-RELATED7 (ATXR7), a putative Set1 class H3K4 methylase, is required for proper FLC expression. The atxr7 mutation partially suppresses the delayed flowering of a FRI-containing line. The rapid flowering of atxr7 is associated with reduced FLC expression and is accompanied by decreased H3K4 methylation and increased H3K27 methylation at FLC. Thus, ATXR7 is required for the proper levels of these histone modifications that set the level of FLC expression to create a vernalization requirement in winter-annual accessions. Previously, it has been reported that lesions in ATX1, which encodes a Trithorax class H3K4 methylase, partially suppress the delayed flowering of winter-annual Arabidopsis. We show that the flowering phenotype of atx1 atxr7 double mutants is additive relative to those of single mutants. Therefore, both classes of H3K4 methylases appear to be required for proper regulation of FLC expression.

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ARABIDOPSIS TRITHORAX-RELATED7 is needed to add a chemical mark that turns on the flowering gene FLOWERING LOCUS C

Abstract

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