Rodríguez-Leal Daniel, León-Martínez Gloria, Abad-Vivero Ursula, Vielle-Calzada Jean-Philippe
Grupo de Desarrollo Reproductivo y Apomixis, Laboratorio Nacional de Genómica para la Biodiversidad y Departamento de Ingeniería Genética de Plantas, Cinvestav Irapuato CP36821 Guanajuato, Mexico.
Centro Interdisciplinario de Investigación para el Desarrollo Integral Regional del Instituto Politécnico Nacional, Unidad Michoacán, CP 59510 Jiquilpan, Mexico.
Plant Cell. 2015 Apr;27(4):1034-45. doi: 10.1105/tpc.114.133009. Epub 2015 Mar 31.
In angiosperms, the transition to the female gametophytic phase relies on the specification of premeiotic gamete precursors from sporophytic cells in the ovule. In Arabidopsis thaliana, a single diploid cell is specified as the premeiotic female gamete precursor. Here, we show that ecotypes of Arabidopsis exhibit differences in megasporogenesis leading to phenotypes reminiscent of defects in dominant mutations that epigenetically affect the specification of female gamete precursors. Intraspecific hybridization and polyploidy exacerbate these defects, which segregate quantitatively in F2 populations derived from ecotypic hybrids, suggesting that multiple loci control cell specification at the onset of female meiosis. This variation in cell differentiation is influenced by the activity of ARGONAUTE9 (AGO9) and RNA-DEPENDENT RNA POLYMERASE6 (RDR6), two genes involved in epigenetic silencing that control the specification of female gamete precursors. The pattern of transcriptional regulation and localization of AGO9 varies among ecotypes, and abnormal gamete precursors in ovules defective for RDR6 share identity with ectopic gamete precursors found in selected ecotypes. Our results indicate that differences in the epigenetic control of cell specification lead to natural phenotypic variation during megasporogenesis. We propose that this mechanism could be implicated in the emergence and evolution of the reproductive alternatives that prevail in flowering plants.
在被子植物中，向雌配子体阶段的转变依赖于从胚珠中的孢子体细胞中指定减数分裂前配子前体。在拟南芥中，单个二倍体细胞被指定为减数分裂前雌配子前体。在这里，我们表明拟南芥生态型在大孢子发生过程中表现出差异，导致出现类似于显性突变缺陷的表型，这些显性突变在表观遗传上影响雌配子前体的指定。种内杂交和多倍体加剧了这些缺陷，这些缺陷在生态型杂种衍生的F2群体中呈数量分离，这表明多个基因座在雌配子减数分裂开始时控制细胞指定。细胞分化的这种变化受AGO9（AGO9）和RNA依赖性RNA聚合酶6（RDR6）的活性影响，这两个基因参与表观遗传沉默，控制雌配子前体的指定。AGO9的转录调控模式和定位在不同生态型之间有所不同，RDR6缺陷胚珠中的异常配子前体与选定生态型中发现的异位配子前体具有相同特征。我们的结果表明，细胞指定的表观遗传控制差异导致大孢子发生过程中的自然表型变异。我们提出，这种机制可能与开花植物中普遍存在的生殖选择的出现和进化有关。
