Di- and Tri- but Not Monomethylation on Histone H3 Lysine 36 Marks Active Transcription of Genes Involved in Flowering Time Regulation and Other Processes in Arabidopsis thaliana

Abstract

Histone lysines can be mono-, di-, or trimethylated, providing an ample magnitude of epigenetic information for transcription regulation. In fungi, SET2 is the sole methyltransferase responsible for mono-, di-, and trimethylation of H3K36. Here we show that in Arabidopsis thaliana, the degree of H3K36 methylation is regulated by distinct methyltransferases. The SET2 homologs SDG8 and SDG26 each can methylate oligonucleosomes in vitro, and both proteins are localized in the nucleus. While the previously reported loss-of-function sdg8 mutants have an early-flowering phenotype, the loss-of-function sdg26 mutants show a late-flowering phenotype. Consistently, several MADS-box flowering repressors are down-regulated by sdg8 but up-regulated by sdg26. The sdg8 but not the sdg26 mutant plants show a dramatically reduced level of both di- and trimethyl-H3K36 and an increased level of monomethyl-H3K36. SDG8 is thus specifically required for di- and trimethylation of H3K36. Our results further establish that H3K36 di- and tri- but not monomethylation correlates with transcription activation. Finally, we show that SDG8 and VIP4, which encodes a component of the PAF1 complex, act independently and synergistically in transcription regulation. Together our results reveal that the deposition of H3K36 methylation is finely regulated, possibly to cope with the complex regulation of growth and development in higher eukaryotes.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/ .

ACKNOWLEDGMENTS

We thank Denise Meyer, Ziqiang Liu, and Juan Gao for help in cytology, RNA preparation, and plasmid construction, respectively. We thank Manfred Heinlein and Alexandre Berr for critically reading the manuscript. We are very grateful to Ru Cao and Yi Zhang (UNC at Chapel Hill, NC) and to Adrien Eberlin and Laszlo Tora (IGBMC, Strasbourg, France) for kindly providing the oligonucleosomes and mononucleosomes, respectively. We thank the Arabidopsis Biological Resource Centre and the Nottingham Arabidopsis Stock Center for providing Arabidopsis seeds.

L.X. is supported by a research training fellowship from the Ministère de la Culture, de l'Enseignement Supérieur et de la Recherche, Luxembourg. Research in W.-H.S.'s laboratory is supported by the Centre National de la Recherche Scientifique.