The evolutionary establishment of apomixis in hybrids of the Ranunculus auricomus complex

无融合生殖是一种通过种子进行的无性生殖，在自然植物种群中多见于多倍体杂交种。然而，杂交和多倍体对发育的实际影响以及向功能性无融合的进化步骤仍不清楚。关于无细胞分裂初始细胞的自发产生，目前提出了两种主要的假说：(1)杂交导致正常情况下控制性发育的基因表达模式发生改变，从而激活胚珠体细胞中的生殖细胞命运；(2)杂交引起减数分裂和大孢子发生的干扰或失败，从而抑制性途径。因此，自然选择倾向于另一种无效的无性途径（逃避不育）。假设多倍体对无融合的定量表达有基因剂量效应，并促进未减数卵细胞的孤雌发育。在一个关于模型系统（毛茛复合体）的前驱项目中，无融合的第一步，即。无孢子的初始细胞，在二倍体和多倍体合成的F1杂交种中自发出现，但只有在多倍体中才产生功能无孢子的种子。在这里，我们提出了一种扩展的实验方法来继续这项研究从兄弟杂交产生的下一代。我们将检验F2兄弟杂交由于遗传控制因素的剂量效应而增加无融合种子形成频率的假设。我们将通过显微镜和种子流式细胞术研究多倍体杂交种和人工多倍体杂交种的雌性发育。为了测试减数分裂干扰与孢子频率的相关性，将使用FISH技术在显微镜下和细胞遗传学上研究雄性和雌性减数分裂。我们期望对两性和无融合生殖发育有更全面的了解，并对植物群体无融合生殖的进化有更深入的了解。

Apomixis, the asexual reproduction via seed, appears in natural plant populations mostly in polyploid hybrids. The actual effects of hybridization and polyploidy on development, however, and evolutionary steps towards functional apomixis are still unclear. Two main lines of hypotheses have been proposed to act as a functional trigger for spontaneous emergence of apomictic initial cells as the first step: (1) hybridization causes alteration of expression patterns of genes controlling normally the sexual development, thereby activating germ cell fate in otherwise somatic cells of the ovule; (2) hybridization causes disturbances or failure of meiosis and megasporogenesis, thereby suppressing the sexual pathway. Thus, selection will favour an alternative, otherwise ineffective asexual pathway (escape from sterility). Polyploidy is hypothesized to have gene dosage effects on quantitative expression of apomixis and to enhance parthenogenetic development of unreduced egg cells. In a precursor project on the model system (Ranunculus auricomus complex) first steps of apomixis, ie. aposporous initial cells, appeared spontaneously in diploid and polyploid synthetic F1 hybrids, but functional apomictic seeds developed only in polyploids. Here we propose an expanded experimental approach to continue this study on the next hybrid generation produced from sibling crosses. We will test the hypothesis that F2 sibling crosses will show increased frequencies of apomictic seed formation because of dosage effects of genetic control factors. We will study female development via microscopy and seed flow cytometry on polyploid hybrids, and on artificially polyploidized diploid hybrids. To test for a correlation of a meiotic disturbance with frequencies of apospory, male and female meiosis will be studied microscopically and cytogenetically with FISH techniques. We expect comprehensive insights into sexual and apomictic development and a deeper understanding of the evolution of apomixis in plant populations.