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

无融合生殖是通过种子进行的无性繁殖，主要出现在自然植物群体中，主要存在于多倍体杂种中。然而，杂交和多倍体对发育和功能无融合生殖的进化步骤的实际影响仍然不清楚。作为第一步，有两条主线的假说被认为是无融合生殖起始细胞自发出现的功能触发因素：(1)杂交导致正常控制性发育的基因表达模式的改变，从而激活胚珠体细胞中生殖细胞的命运；(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，选择将有利于一种替代的、否则无效的无性途径(逃避不孕)。多倍体被认为对无融合生殖的数量表达有基因剂量效应，并促进未减数卵细胞的孤雌生殖发育。在模式系统(毛滴草复合体)的前体项目中，无融合生殖的第一步，即。无融合生殖起始细胞在二倍体和多倍体合成F1中自发出现，但功能无融合生殖种子仅在多倍体中发育。在这里，我们提出了一种扩展的实验方法，以继续这项研究的下一个杂交世代产生的兄弟姐妹杂交。我们将验证这样的假设，即由于遗传控制因素的剂量效应，F2同胞杂交将显示出更高的无融合生殖种子形成频率。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二倍体杂交种的雌性发育。为了测试减数分裂障碍与无孢子分裂频率的相关性，将用FISH技术对雄性和雌性减数分裂进行显微镜和细胞遗传学研究。我们期望对有性生殖和无融合生殖发育有全面的见解，并对植物种群中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.