title: Conserved imprinting associated with unique epigenetic signatures in the Arabidopsis genus.
abstract: In plants, imprinted gene expression occurs in endosperm seed tissue and is sometimes associated with differential DNA methylation between maternal and paternal alleles(1). Imprinting is theorized to have been selected for because of conflict between parental genomes in offspring(2), but most studies of imprinting have been conducted in Arabidopsis thaliana, an inbred primarily self-fertilizing species that should have limited parental conflict. We examined embryo and endosperm allele-specific expression and DNA methylation genome-wide in the wild outcrossing species Arabidopsis lyrata. Here we show that the majority of A. lyrata imprinted genes also exhibit parentally biased expression in A. thaliana, suggesting that there is evolutionary conservation in gene imprinting. Surprisingly, we discovered substantial interspecies differences in methylation features associated with paternally expressed imprinted genes (PEGs). Unlike in A. thaliana, the maternal allele of many A. lyrata PEGs was hypermethylated in the CHG context. Increased maternal allele CHG methylation was associated with increased expression bias in favour of the paternal allele. We propose that CHG methylation maintains or reinforces repression of maternal alleles of PEGs. These data suggest that the genes subject to imprinting are largely conserved, but there is flexibility in the epigenetic mechanisms employed between closely related species to maintain monoallelic expression. This supports the idea that imprinting of specific genes is a functional phenomenon, and not simply a byproduct of seed epigenomic reprogramming.
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142, USA.
authors.forename: Maja
authors.initials: M
authors.lastname: Klosinska
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142, USA.|Computational and Systems Biology Graduate Program, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Colette L
authors.identifier: 0000-0002-2177-2216
authors.initials: CL
authors.lastname: Picard
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142, USA.|Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Mary
authors.identifier: 0000-0003-2280-1522
authors.initials: M
authors.lastname: Gehring
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D019175:DNA Methylation; D056625:Endosperm; D044127:Epigenesis, Genetic; D019143:Evolution, Molecular; D018506:Gene Expression Regulation, Plant; D018392:Genomic Imprinting