A search for novel genes involved in meiosis in Arabidopsis thaliana

Abstract

Meiosis is a two-round reductional cell division which requires modifications to the mitotic cell cycle machinery. The mammalian meiosis-specific master regulator MEIKIN and its functional homologues in budding yeast and fission yeast play an essential function during meiosis. This project attempts to find their Arabidopsis functional homologue, which has not yet been identified. A candidate gene AT5G64540, hereby called MMEG1 (MALE MEIOSIS EXPRESSED GENE 1), was identified through phylogenetic distant homology analysis. The mmeg1 mutant shows an abnormal chromosome morphology, which is also reflected in reduced fertility. Additionally, in its double mutant with the mutant for cell cycle regulator AtOSD1, we observe meiotic exit after prophase, resulting in polyploid progeny and a decrease in fertility. However, unlike MEIKIN and its functional homologues, AtMMEG1 does not localise on the meiotic kinetochore and instead forms dispersed foci in the cytoplasm. Moreover, it also does not appear to have any effect on the orientation of sister kinetochores to the same spindle pole during meiosis I, which is a key function of MEIKIN, challenging the role of MMEG1 as its homologue. We also studied three other uncharacterised highly expressed genes in meiocytes to identify their potential role in meiosis but did not recognise any defect in meiosis in their mutants. In conclusion, we report the finding of a novel Arabidopsis thaliana meiotic gene MMEG1, which has no clear sequence homologue beyond Brassicaceae but plays a key role in meiotic cell cycle progression and meiotic chromosome morphology.