The evolution of RNA helicases and their roles for plant sexual and apomictic reproduction

高等植物采用不同的策略来确保成功繁殖，包括种子的有性和无性形成(无融合生殖)。与有性生殖不同，无融合生殖产生克隆后代。利用无融合生殖技术生产作物种子具有巨大的潜力，因为优良的基因类型可以在后代中保持下去。虽然无融合生殖在主要作物中自然不存在，但工程上的无融合生殖仍然是一个挑战。情况就是这样，尽管从科学和应用的角度都有很高的兴趣，但到目前为止，允许无融合生殖建立的进化过程和控制无融合生殖的分子程序仍然没有被很好地理解。越来越多的证据表明，复杂的基因调控程序严格控制生殖谱系的发展。无融合生殖的基础很可能是性途径的放松。现在，我们通过对羊草属有性和无融合生殖材料的比较转录组分析，发现了细胞周期控制、转录和转录后调控存在差异的进一步证据。重要的是，新的无融合生殖候选基因被发现，这些基因可能与控制有性生殖的基因有关。此外，RNA解旋酶在无融合生殖调控中的意义已经被提出。重要的是，携带MNEME(MEM)突变等位基因的植物在拟南芥中显示出无融合生殖的元素。我们现在发现了这个基因家族的其他成员，突变会导致生殖发育过程中的缺陷。为了进一步了解RNA解旋酶在无融合生殖中的作用及其进化，我们对几个有性和无融合生殖Boechera材料的等位基因变体进行了测序。根据不同的RNA解旋酶对生殖的重要性，不同的RNA解旋酶表现出明显的等位变异差异。虽然对发育过程至关重要的解旋酶几乎没有变化，但包括MEM在内的其他解旋酶的等位基因差异更大，可能对无融合生殖具有重要意义。拟议项目的目的是更全面地了解无融合生殖的基因调控基础，特别是RNA解旋酶在这一过程中的作用。为此，将结合不同的方法来(I)将转录分析扩展到配子发生的早期阶段，以加深我们对有性和无融合生殖中基因表达调控的理解，(Ii)扩大对选定的RNA解旋酶的功能分析，重点是鉴定突变体中无融合生殖的特征，以及(Iii)通过用有性和无融合生殖的等位变异来补充突变体来测试无融合生殖的等位变异的功能含义。这项研究将有助于理解控制有性生殖和无融合生殖的分子过程及其进化的各个方面。

Higher plants employ different strategies to ensure successful reproduction, including sexual and asexual formation of seeds (apomixis). Unlike sexual reproduction, apomixis gives rise to clonal offspring. Harnessing of apomixis for crop seed production has outstanding potential, as superior genotypes could be maintained in subsequent generations. While apomixis is naturally not represented in major crops, engineering of apomixis remains a challenge. This is the case, as despite high interest from scientific as well as applied perspectives, the evolutionary processes that allowed apomixis to establish and the molecular programs governing apomictic reproduction are still not well understood to date.Increasing evidence suggests that a complex gene regulatory program tightly controls the development of reproductive lineages. And the basis of apomixis is likely a deregulation of the sexual pathway. Consistently, we now identified further evidence for differences in cell cycle control, transcriptional and posttranscriptional regulation by comparative transcriptome analysis of sexual and apomictic accessions of the genus Boechera. Importantly, new candidate genes for apomixis were uncovered that presumably relate to genes controlling sexual reproduction. Moreover, implications for RNA helicases in regulation of apomixis have previously been suggested. Importantly, plants carrying mutant alleles of MNEME (MEM) show an element of apomixis in Arabidopsis. We now identified additional members of this gene family, for which mutations lead to defects during reproductive development. To gain further insights into the roles of RNA helicases for apomixis and into aspects of their evolution, we sequenced allelic variants of several sexual and apomictic Boechera accessions. In line with the importance of different RNA helicases for reproduction, different RNA helicases showed distinct divergence of allelic variants. While helicases that are supposedly crucial for developmental processes show little variation, greater allelic divergence in others, including MEM, might be of importance for apomixis. The aim of the proposed project is to gain more comprehensive insights into the gene regulatory basis of apomixis and in particular the roles of RNA helicases in this process. To this aim different approaches will be integrated to (I) extend transcriptional analysis to early stages of gametogenesis to deepen our understanding of the regulation of gene expression in sexual versus apomictic Boechera, to (II) broaden functional analysis of selected RNA helicases with emphasis on the identification of features of apomixis in mutants, and (III) by testing functional implications of allelic variants from apomicts by complementing mutant lines with allelic variants from sexual and apomictic Boechera. This study will significantly contribute to an understanding of the molecular processes governing sexual and apomictic plant reproduction and aspects of their evolution.