OsMND1 regulates early meiosis and improves the seed set rate in polyploid rice

The meiotic processes of most polyploid rice (Oryza sativa) are genetically abnormal, leading to low pollen fertility, which results in low seed set rates. Some polyploid meiosis stability (PMeS) lines with high seed set rates have been bred but their meiotic mechanisms remain unknown. In this study, we investigated the function of OsMND1 regulated polyploid rice meiosis. OsMND1 localized in the nucleus, and its expression level in panicles of PMeS line HN2026-4x was higher than in HN2026-2x and the other lines without the PMeS background. OsMND1's overexpression improved pollen fertility and viability, early normal embryo development and the seed set rate in Balilla-4x. However, OsMND1 RNAi in PMeS line HN2026-4x impeded pollen and embryo development significantly. The results of chromosome behavior analyses indicated that OsMND1 participates in stabilizing meiosis by maintaining the balance of pairing, synapsis and recombination during early meiosis. Many univalent, trivalent, and even multivalent systems appeared in the OsMND1 RNAi line, resulting in the presence of many lagging chromosomes. The outcome indicated that OsMND1 plays a critical role in stabilizing meiosis, improving pollen fertility and reducing early embryo abortions, ultimately increasing the seed set rate. Additionally, OsMND1 affected some key meiosis-related gene expression levels. These results raise interesting issues in polyploid breeding theory and application, which require integrated solutions in the future.