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

Abstract

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.

Chromosome Pairing in Polyploid Grasses

“…These two lines display regular meiotic behavior, with bivalents and quadrivalents. The existence of genetic chromosome pairing PMeS control was confirmed by the persistent meiotic stability of the two lines even after several generations (Xiong et al, 2019).…”

Transcriptome and Gene Editing Analyses Reveal MOF1a Defect Alters the Expression of Genes Associated with Tapetum Development and Chromosome Behavior at Meiosis Stage Resulting in Low Pollen Fertility of Tetraploid Rice

“…In addition, loss function of MOF1a also increased the frequency of PMCs with abnormal chromosome behaviors in seven stage of meiosis, and the most common abnormality was the straggle chromosome. In a previous study, many mutants of meiosis-related genes, such as ZIP4 , OsREC8 , MRE11 , OsSGO1 , HEI10 , OsDMC1 , and OsMND1, caused similar straggle chromosomes during meiosis process because of abnormal homologous synapsis or double strand break [ 65 , 66 , 67 , 68 , 69 , 70 , 71 ]. Disorder of microtube distribution is also considered a key reason of chromosome behaviors [ 9 , 72 ].…”

Fertile Tetraploids: New Resources for Future Rice Breeding?

“…These results suggest that stable meiosis, timely tapetum degradation, and normal mitochondrial development were the critical factors ensuring the high pollen fertility of PMeS lines (He et al, 2010). Recently, Xiong et al (2019) revealed that the rice homolog of the gene MND1, which plays a role in meiosis in yeast and Arabidopsis, also plays a crucial role in improving the seed set rate in PMeS lines. They showed that the OsMND1 expression level in panicles of a PMeS line was higher than in the diploid lines or in the other autotetraploid line with low seed set rate and OsMND1 overexpression improved pollen fertility and seed set.…”

“…They showed that the OsMND1 expression level in panicles of a PMeS line was higher than in the diploid lines or in the other autotetraploid line with low seed set rate and OsMND1 overexpression improved pollen fertility and seed set. The meiotic behavioral observations suggested that the effects of OsMND1 might be maintaining the balance of synapsis and recombination (Xiong et al, 2019). However, it is still unknown why the expression level of OsMND1 was lower in autotetraploid line with low seed set rate than the PMeS line.…”

“…However, it is still unknown why the expression level of OsMND1 was lower in autotetraploid line with low seed set rate than the PMeS line. More research is necessary for a full understanding of the molecular mechanism of normal meiosis in PMeS lines (Xiong et al, 2019). The other autotetraploid rice varieties with high seed and pollen fertilities were named the Neo-Tetraploid lines by Guo et al (2017).…”