Spillane Charles, Schmid Karl J, Laoueillé-Duprat Sylvia, Pien Stéphane, Escobar-Restrepo Juan-Miguel, Baroux Célia, Gagliardini Valeria, Page Damian R, Wolfe Kenneth H, Grossniklaus Ueli
Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, CH-8008 Zürich, Switzerland.
Nature. 2007 Jul 19;448(7151):349-52. doi: 10.1038/nature05984.
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.
在哺乳动物和种子植物中，一部分基因受基因组印记调控，即一个等位基因的活性取决于其亲本来源。亲本冲突理论认为，基因组印记是在胚胎滋养组织（胎盘和胚乳）出现后进化而来的，这导致了基因组内关于从母体向后代分配营养物质的亲本冲突。据预测，通过亲本冲突驱动的拮抗协同进化产生的印记基因，应受到正向达尔文选择。在此，我们表明，对种子发育至关重要的印记植物基因MEA，起源于3500万至8500万年前的一次全基因组复制事件。复制后，MEA经历了与新功能化及亲本冲突理论相符的正向达尔文选择。MEA在异交物种琴叶拟南芥中继续快速进化，但在自花受精物种拟南芥中并非如此，因为在拟南芥中亲本冲突减少。MEA的旁系同源基因SWINGER（SWN；也称为EZA1）没有印记，且在强烈的纯化选择下进化，因为它可能保留了共同前体基因的祖先功能。MEA的进化表明十字花科内基因组印记起源较晚，而印记被认为在哺乳动物谱系中起源较早。
