title: Sexual epigenetics: gender-specific methylation of a gene in the sex determining region of Populus balsamifera.
abstract: Methylation has frequently been implicated in gender determination in plants. The recent discovery of the sex determining region (SDR) of balsam poplar, Populus balsamifera, pinpointed 13 genes with differentiated X and Y copies. We tested these genes for differential methylation using whole methylome sequencing of xylem tissue of multiple individuals grown under field conditions in two common gardens. The only SDR gene to show a marked pattern of gender-specific methylation is PbRR9, a member of the two component response regulator (type-A) gene family, involved in cytokinin signalling. It is an ortholog of Arabidopsis genes ARR16 and ARR17. The strongest patterns of differential methylation (mostly male-biased) are found in the putative promoter and the first intron. The 4th intron is strongly methylated in both sexes and the 5th intron is unmethylated in both sexes. Using a statistical learning algorithm we find that it is possible accurately to assign trees to gender using genome-wide methylation patterns alone. The strongest predictor is the region coincident with PbRR9, showing that this gene stands out against all genes in the genome in having the strongest sex-specific methylation pattern. We propose the hypothesis that PbRR9 has a direct, epigenetically mediated, role in poplar sex determination.
authors.affiliation: Department of Biology, University of Toronto Missisauga, Mississauga ON, L5L 1C6, Canada.
authors.forename: Katharina
authors.initials: K
authors.lastname: Bräutigam
authors.affiliation: Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon SK, S7N OX2, Canada.
authors.forename: Raju
authors.initials: R
authors.lastname: Soolanayakanahally
authors.affiliation: Department of Biological Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada.
authors.forename: Marc
authors.initials: M
authors.lastname: Champigny
authors.affiliation: Department of Wood Science, University of British Columbia, 4030-2424 Main Mall, Vancouver BC, V6T 1Z4, Canada.
authors.forename: Shawn
authors.initials: S
authors.lastname: Mansfield
authors.affiliation: Department of Botany, University of British Columbia, Vancouver BC, V6T 1Z4, Canada.
authors.forename: Carl
authors.initials: C
authors.lastname: Douglas
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph ON N1G 2W1, Canada.
authors.forename: Malcolm M
authors.initials: MM
authors.lastname: Campbell
authors.affiliation: Department of Botany, University of British Columbia, Vancouver BC, V6T 1Z4, Canada.
authors.forename: Quentin
authors.initials: Q
authors.lastname: Cronk
mesh_terms: D019175:DNA Methylation / Q000235:genetics*; D044127:Epigenesis, Genetic / Q000235:genetics*; D057890:Epigenomics / Q000379:methods; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D018745:Genome, Plant / Q000235:genetics; D032107:Populus / Q000235:genetics*