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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

SET DOMAIN GROUP25 Encodes a Histone Methyltransferase and Is Involved in FLOWERING LOCUS C Activation and Repression of Flowering^1,[W],[OA]

Institut de Biologie Moléculaire des Plantes du Centre National de la Recherche Scientifique, Université de Strasbourg, 67084 Strasbourg cedex, France (A.B., L.X., J.G., V.C., W.-H.S.); Centre de Recherche Public de la Santé, L–1526 Luxembourg, Luxembourg (A.S.); and State Key Laboratory of Genetic Engineering, Department of Biochemistry, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China (J.G., A.D.)

Covalent modifications of histone lysine residues by methylation play key roles in the regulation of chromatin structure and function. In contrast to H3K9 and H3K27 methylations that mark repressive states of transcription and are absent in some lower eukaryotes, H3K4 and H3K36 methylations are considered as active marks of transcription and are highly conserved in all eukaryotes from yeast (Saccharomyces cerevisiae) to Homo sapiens. Paradoxically, protein complexes catalyzing H3K4 and H3K36 methylations are less-extensively characterized in higher eukaryotes, particularly in plants. Arabidopsis (Arabidopsis thaliana) contains 12 SET DOMAIN GROUP (SDG) proteins phylogenetic classified to Trithorax Group (TrxG) and thus potentially involved in H3K4 and H3K36 methylations. So far only some genes of this family had been functionally characterized. Here we report on the genetic and molecular characterization of SDG25, a previously uncharacterized member of the Arabidopsis TrxG family. We show that the loss-of-function mutant sdg25-1 has an early flowering phenotype associated with suppression of FLOWERING LOCUS C (FLC) expression. Recombinant SDG25 proteins could methylate histone H3 from oligonucleosomes and mutant sdg25-1 plants showed weakly reduced levels of H3K36 dimethylation at FLC chromatin. Interestingly, sdg25-1 transcriptome shared a highly significant number of differentially expressed genes with that of sdg26-1, a previously characterized mutant exhibiting late-flowering phenotype and elevated FLC expression. Taken together, our results provide, to our knowledge, the first demonstration for a biological function of SDG25 and reveal additional layers of complexity of overlap and nonoverlap functions of the TrxG family genes in Arabidopsis.

² These authors contributed equally to the article.

³ Present address: National Key Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai 200032, China.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Wen-Hui Shen (wen-hui.shen{at}ibmp-ulp.u-strasbg.fr).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.143941

^* Corresponding author; e-mail wen-hui.shen{at}ibmp-ulp.u-strasbg.fr.

Received June 30, 2009; accepted August 26, 2009; published September 2, 2009.