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

无融合生殖是植物通过种子进行无性繁殖的过程，主要存在于多倍体杂种中。然而，杂交和多倍体对发育的实际影响，以及功能性无融合生殖的进化步骤仍然不清楚。作为无融合生殖起始细胞自发出现的第一步，已经提出了两条主要的假说：（1）杂交引起正常控制性发育的基因的表达模式的改变，从而激活胚珠的体细胞中的生殖细胞命运;（2）杂交导致减数分裂和大孢子发生的干扰或失败，从而抑制有性途径。因此，选择将有利于另一种选择，否则无效的无性途径（逃离不育）。多倍性被假设为对无融合生殖的定量表达具有基因剂量效应，并增强未减数卵细胞的孤雌发育。在模型系统（耳头毛茛复合体）的前期项目中，无融合生殖的第一步，即。在二倍体和多倍体人工合成的F1杂种中自发地出现无孢子生殖的原始细胞，但功能性无融合生殖种子仅在多倍体中发育。在这里，我们提出了一个扩大的实验方法，继续这项研究的下一代杂交产生的同胞杂交。我们将测试的假设，即F2同胞杂交将显示无融合生殖种子形成的频率增加，因为遗传控制因素的剂量效应。我们将通过显微镜和种子流式细胞术研究多倍体杂种和人工多倍体化二倍体杂种的雌性发育。为了检测减数分裂障碍与无孢子生殖频率的相关性，将用显微镜和FISH技术对雄性和雌性减数分裂进行细胞遗传学研究。我们期望全面了解性和无融合生殖的发展和更深入地了解植物种群中的无融合生殖的进化。

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.