Microscopic and transcriptomic comparison of the ovaries between the sexual and apomictic dandelions reveals the developmental process and gene regulation in regard to apomixis

The Russian dandelion ( Taraxacum kok-saghyz Robin, TKS) is the most potential alternative rubber-producing crop. Nevertheless, self-incompatibility (SI) currently presents as a main obstacle for industrial cultivation and seed production of TKS. The transfer of apomixis and its effective utilization in TKS is important for overcoming SI and developing TKS as an industrial crop. Genetic studies indicate that the apomixis is a three-event process in the dandelion species, namely diplospory, parthenogenesis and endosperm autonomy, which are controlled by the independent loci in the apomictic dandelion genomes. However, the developmental and molecular mechanisms of apomixis in dandelion remain less understood. In this study, we compared the developmental process and gene expression profile in the developing ovaries between the TKS and apomictic dandelion species T. spadiceum . The microscopic observation showed that the apomixis was initiated by the formation of the modified egg cell and central cell without chromosome reduction, which further autonomously underwent embryogenesis and endosperm formation, leading to formation of asexual seeds. The transcriptomic comparison in the developing ovaries between the sexual and apomixis dandelion plants showed significantly differential expression of the genes related to meiosis, cell cycle control, embryogenesis, endosperm formation and auxin signaling, which could be associated with the process of apomixis in the dandelion species. The results provide novel insights into the developmental process and gene regulation of apomixis in the dandelion species and lay a foundation for introducing apomixis into TKS. • The megaspore mother cell underwent mitosis in the apomictic dandelions. • The cell cycle control was different between the sexual and apomictic dandelions. • The genes of embryogenesis were upregulated in the ovaries of apomictic dandelions. • Auxin signaling may play important roles in the apomixis of dandelions.