RESUMO
The Arabidopsis Flowering Locus C (FLC) protein is a repressor of flowering regulated by genes in the autonomous and vernalization pathways. Previous genetic and transgenic data have suggested that FLC acts by repressing expression of the floral integrator genes SOC1 and FT. We have taken an in vivo approach to determine whether the FLC protein interacts directly with potential DNA targets. Using chromatin immunoprecipitation, we have shown that FLC binds to a region of the first intron of FT that contains a putative CArG box, and have confirmed that FLC binds to a CArG box in the promoter of the SOC1 gene. MADS box proteins are thought to bind their DNA targets as dimers or higher-order multimers. We have shown that FLC is a component of a multimeric protein complex in vivo and that more than one FLC polypeptides can be present in the complex.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Cromatina/metabolismo , Proteínas de Domínio MADS/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Sequência de Bases , Cromatina/genética , Primers do DNA , Proteínas de Domínio MADS/genética , Substâncias Macromoleculares/metabolismo , Proteínas Recombinantes/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
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. In both cases, there is a reduction of histone H3 trimethyl-lysine 4 (K4) and acetylation of both histones H3 and H4 around the promoter-translation start of FLC. The expression of the two genes flanking FLC is also repressed in both conditions and repression is associated with decreased histone H3 acetylation. The changes in histone modifications at the FLC gene cluster, which are similar in vernalized plants and in plants with reduced DNA methylation, must arise by different mechanisms. VERNALIZATION 1, VERNALIZATION 2 and VERNALIZATION INSENSITIVE 3 modulate FLC expression in vernalized plants; these proteins play no role in the downregulation of FLC in plants with low levels of DNA methylation. Chimeric FLC::GUS transgenes respond to vernalization but these same transgenes show a position-dependent response to low levels of DNA methylation. In plants with reduced DNA methylation, expression of the five MADS AFFECTING FLOWERING (MAF) genes is repressed, suggesting that DNA methylation alters the expression of a trans-acting regulator common to FLC and members of the related MAF gene family. Our observations suggest that DNA methylation is not part of the vernalization pathway.
