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

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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.