Polyploid hybrid rice (Oryza sativa) has great potential for increasing yields. However, hybrid rice depends on male fertility and its regulation, which is less well studied in polyploid rice than in diploid rice. We previously identified a MYB transcription factor, MORE FLORET1 (MOF1), whose mutation causes male sterility in neo-tetraploid rice. MOF1 expression in anthers peaks at anther Stage 7 (S7) and progressively decreases to low levels at S10. However, it remains unclear how the dynamics of MOF1 expression contribute to male fertility. Here, we carefully examined anther development in both diploid and tetraploid mof1 rice mutants, as well as lines ectopically expressing MOF1 in a temporal manner. MOF1 mutations caused delayed degeneration of the tapetum and middle layer of anthers and aberrant pollen wall organization. Ectopic MOF1 expression at later stages of anther development led to retarded cytoplasmic reorganization of tapetal cells. In both cases, pollen grains were aborted and seed production was abolished, indicating that precise control of MOF1 expression is essential for male reproduction. We demonstrated that five key tapetal genes, CYP703A3 (CYTOCHROME P450 HYDROXYLASE 703A3), OsABCG26 (Oryza sativa ATP BINDING CASSETTE G26), PTC1 (PERSISTENT TAPETAL CELL1), PKS2 (POLYKETIDE SYNTHASE 2), and OsABCG15 (Oryza sativa ATP BINDING CASSETTE G15), exhibit expression patterns opposite to those of MOF1 and are negatively regulated by MOF1. Moreover, DNA affinity purification sequencing (DAP-seq), luciferase activity assays, and electrophoretic mobility shift assays indicated that MOF1 binds directly to the PKS2 promoter for transcriptional repression. Our results provide a mechanistic basis for the regulation of male reproduction by MOF1 in both diploid and tetraploid rice. This study will facilitate the development of polyploid male sterile lines, which are useful for breeding of polyploid hybrid rice.

中文翻译：

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FLORET1 通过负调控二倍体和四倍体水稻中关键绒毡层基因来控制花药发育

多倍体杂交水稻（Oryza sativa）具有巨大的增产潜力。然而，杂交水稻依赖于雄性生育力及其调节，与二倍体水稻相比，对多倍体水稻的研究较少。我们之前鉴定了一种 MYB 转录因子 MORE FLORET1 (MOF1)，其突变导致新四倍体水稻雄性不育。花药中的 MOF1 表达在花药阶段 7 (S7) 达到峰值，并在 S10 逐渐降低至低水平。然而，MOF1 表达动态如何影响男性生育力仍不清楚。在这里，我们仔细检查了二倍体和四倍体 mof1 水稻突变体以及以时间方式异位表达 MOF1 的品系的花药发育。 MOF1突变导致绒毡层和花药中层的延迟退化以及花粉壁组织的异常。花药发育后期的异位 MOF1 表达导致绒毡层细胞的细胞质重组延迟。在这两种情况下，花粉粒都被败育，种子生产被取消，这表明 MOF1 表达的精确控制对于雄性繁殖至关重要。我们证明了五个关键绒毡层基因：CYP703A3 (CYTOCHROME P450 HYDROXYLASE 703A3)、OsABCG26 (Oryza sativa ATP BINDING CASSETTE G26)、PTC1 (PERSISTENT TapETAL CELL1)、PKS2 (POLYKETIDE SYNTHASE 2) 和 OsABCG15 (Oryza sativa ATP BINDING CASSETTE G1) 5） ，表现出与 MOF1 相反的表达模式，并受到 MOF1 的负调控。此外，DNA 亲和纯化测序 (DAP-seq)、荧光素酶活性测定和电泳迁移率变动测定表明 MOF1 直接与 PKS2 启动子结合以抑制转录。我们的结果为 MOF1 在二倍体和四倍体水稻中调节雄性生殖提供了机制基础。该研究将促进多倍体雄性不育系的开发，这对于多倍体杂交水稻的育种是有用的。