Fixation of hybrid vigor in rice: synthetic apomixis generated by genome editing

Apomixis is an asexual reproduction process in which clonal seeds are formed without meiosis and fertilization. Because of its potential in permanently preserving hybrid vigor, apomixis has attracted a great deal of interests from plant biologists and the seed industry. However, despite of decades of effort, introgression of apomixis traits from wild relatives into major crops has remained unsuccessful. Therefore, synthetic apomixis has been proposed as an alternative to fix hybrid vigor. In this article, I present the development of the MiMe (Mitosis instead of Meiosis), which turns meiosis into mitosis and leads to the production of clonal gametes. Apomixis-like clonal seeds are generated when MiMe plants are crossed to special genome elimination lines, which contain an altered centromere-specific histone 3 (CENH3). Furthermore, induction of haploid plants from egg cells can be achieved by either egg cell-specific expression of BABY BOOM1 (BBM1), or disruption of MATRILINEAL (MTL) using CRISPR/Cas9 gene-editing technology. Synthetic apomixis is established and clonal seeds are produced by simultaneous engineering MiMe with altering BBM1 expression or MTL disruption. Finally, I discuss how to further improve the apomixis strategy and its applications in crop breeding.