title: A histone methylation-dependent DNA methylation pathway is uniquely impaired by deficiency in Arabidopsis S-adenosylhomocysteine hydrolase.
abstract: S-adenosylhomocysteine hydrolase (SAH) is a key enzyme in the maintenance of methylation homeostasis in eukaryotes because it is needed to metabolize the by-product of transmethylation reactions, S-adenosylhomocysteine (AdoHcy), which causes by-product inhibition of methyltransferases (MTase's). Complete loss of SAH function is lethal. Partial loss of SAH function causes pleiotropic effects including developmental abnormalities and reduced cytosine methylation. Here we describe a novel partial-function missense allele of the Arabidopsis SAH1 gene that causes loss of cytosine methylation specifically in non-CG contexts controlled by the CMT3 DNA MTase and transcriptional reactivation of a silenced reporter gene, without conferring developmental abnormalities. The CMT3 pathway depends on histone H3 lysine 9 methylation (H3 mK9) to guide DNA methylation. Our results suggest that this pathway is uniquely sensitive to SAH impairment because of its requirement for two transmethylation reactions that can both be inhibited by AdoHcy. Our results further suggest that gene silencing pathways involving an interplay between histone and DNA methylation in other eukaryotes can be selectively impaired by controlled SAH downregulation.
authors.affiliation: Department of Biochemistry and Molecular Biology, Johns Hopkins University, Bloomberg School of Public Health, Baltimore, Maryland 21205, USA.
authors.forename: Lori
authors.initials: L
authors.lastname: Mull
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Ebbs
authors.forename: Judith
authors.initials: J
authors.lastname: Bender
mesh_terms: D043383:Adenosylhomocysteinase / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics; D000483:Alleles; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors / Q000235:genetics; D019175:DNA Methylation; D018744:DNA, Plant / Q000378:metabolism; D015257:DNA-Cytosine Methylases / Q000037:antagonists & inhibitors / Q000235:genetics; D020868:Gene Silencing; D017343:Genes, Plant; D017930:Genes, Reporter; D005816:Genetic Complementation Test; D000076983:Histone Methyltransferases; D011495:Histone-Lysine N-Methyltransferase / Q000037:antagonists & inhibitors / Q000235:genetics; D006657:Histones / Q000378:metabolism; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D011496:Protein Methyltransferases; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012435:S-Adenosylhomocysteine / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015533:Transcriptional Activation
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; D006657:Histones; D012435:S-Adenosylhomocysteine; D015257:DNA-Cytosine Methylases; D000076983:Histone Methyltransferases; D011496:Protein Methyltransferases; C429766:CMT3 protein, Arabidopsis; D011495:Histone-Lysine N-Methyltransferase; C515275:SUVH3 protein, Arabidopsis; D043383:Adenosylhomocysteinase