title: Positive darwinian selection at the imprinted MEDEA locus in plants.
abstract: In mammals and seed plants, a subset of genes is regulated by genomic imprinting where an allele's activity depends on its parental origin. The parental conflict theory suggests that genomic imprinting evolved after the emergence of an embryo-nourishing tissue (placenta and endosperm), resulting in an intragenomic parental conflict over the allocation of nutrients from mother to offspring. It was predicted that imprinted genes, which arose through antagonistic co-evolution driven by a parental conflict, should be subject to positive darwinian selection. Here we show that the imprinted plant gene MEDEA (MEA), which is essential for seed development, originated during a whole-genome duplication 35 to 85 million years ago. After duplication, MEA underwent positive darwinian selection consistent with neo-functionalization and the parental conflict theory. MEA continues to evolve rapidly in the out-crossing species Arabidopsis lyrata but not in the self-fertilizing species Arabidopsis thaliana, where parental conflicts are reduced. The paralogue of MEA, SWINGER (SWN; also called EZA1), is not imprinted and evolved under strong purifying selection because it probably retained the ancestral function of the common precursor gene. The evolution of MEA suggests a late origin of genomic imprinting within the Brassicaceae, whereas imprinting is thought to have originated early within the mammalian lineage.
authors.affiliation: Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, CH-8008 Zürich, Switzerland. grossnik@botinst.uzh.ch
authors.forename: Charles
authors.initials: C
authors.lastname: Spillane
authors.forename: Karl J
authors.initials: KJ
authors.lastname: Schmid
authors.forename: Sylvia
authors.initials: S
authors.lastname: Laoueillé-Duprat
authors.forename: Stéphane
authors.initials: S
authors.lastname: Pien
authors.forename: Juan-Miguel
authors.initials: JM
authors.lastname: Escobar-Restrepo
authors.forename: Célia
authors.initials: C
authors.lastname: Baroux
authors.forename: Valeria
authors.initials: V
authors.lastname: Gagliardini
authors.forename: Damian R
authors.initials: DR
authors.lastname: Page
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Wolfe
authors.forename: Ueli
authors.initials: U
authors.lastname: Grossniklaus
mesh_terms: D000483:Alleles; D000818:Animals; D017360:Arabidopsis / Q000196:embryology / Q000235:genetics* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics*; D019143:Evolution, Molecular; D020440:Gene Duplication; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics*; D018745:Genome, Plant / Q000235:genetics; D018392:Genomic Imprinting / Q000235:genetics*; D008322:Mammals / Q000235:genetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D012641:Selection, Genetic
chemical_list: D029681:Arabidopsis Proteins; C111712:MEA protein, Arabidopsis