Wu Jinwen, Chen Lin, Shahid Muhammad Qasim, Chen Minyi, Dong Qinglei, Li Jirui, Xu Xiaosong, Liu Xiangdong
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, South China Agricultural University, Guangzhou, 510642, China.
Rice (N Y). 2017 Dec 2;10(1):49. doi: 10.1186/s12284-017-0188-8.
Intersubspecific autotetraploid rice hybrids possess high hybrid vigor; however, low pollen fertility is a critical hindrance in its commercial utilization. Our previous study demonstrated that polyploidy could increase the multi-loci interaction and cause high pollen abortion in autotetraploid rice hybrids. However, there is little known about the critical role of pollen sterility locus or loci in the intersubspecific hybrids. We developed autotetraploid rice hybrids harboring heterozygous genotypes (S S S S ) at different pollen sterility loci by using the near isogenic lines of Taichung65-4×. Moreover, autotetraploid lines carrying double neutral genes, Sa and Sb , were used to assess their effect on fertility restoration.
Cytological studies showed that the deleterious genetic interactions at Sa and Sb pollen sterility loci resulted in higher pollen sterility (76.83%) and abnormal chromosome behavior (24.59%) at metaphase I of meiosis in autotetraploid rice hybrids. Transcriptome analysis revealed 1092 differentially expressed genes (DEG) in a hybrid with the pervasive interactions at Sa and Sb pollen sterility loci, and most of the genes (about 83%) exhibited down regulation. Of the DEG, 60 were associated with transcription regulation and 18 genes were annotated as meiosis-related genes. Analysis on the hybrids developed by using autotetraploid rice harboring double neutral genes, Sa and Sb , revealed normal pollen fertility, and transcriptome analysis showed non-significant difference in number of DEG among different hybrids.
Our finding revealed that pervasive interactions at Sa and Sb pollen sterility loci cause high sterility in the autotetraploid hybrids that lead to the down-regulation of important meiosis-related genes and transcription regulation factors. Moreover, we also found that the hybrids sterility could be overcome by double neutral genes, Sa and Sb , in autotetraploid rice hybrids. The present study provided a strong evidence for the utilization of heterosis in autotetraploid rice hybrids.
亚种间同源四倍体水稻杂种具有较高的杂种优势；然而，低花粉育性是其商业利用的关键障碍。我们之前的研究表明，多倍体可增加多位点互作并导致同源四倍体水稻杂种中出现高花粉败育现象。然而，关于花粉不育位点在亚种间杂种中的关键作用，人们所知甚少。我们通过使用台中65-4×的近等基因系，培育出了在不同花粉不育位点具有杂合基因型（S₁S₂S₃S₄）的同源四倍体水稻杂种。此外，携带双中性基因Saⁿ和Sbⁿ的同源四倍体系被用于评估它们对育性恢复的影响。
细胞学研究表明，在同源四倍体水稻杂种减数分裂中期I，Sa和Sb花粉不育位点处的有害遗传互作导致了较高的花粉不育率（76.83%）和异常染色体行为（24.59%）。转录组分析显示，在具有Sa和Sb花粉不育位点普遍互作的杂种中，有1092个差异表达基因（DEG），且大多数基因（约83%）表现出下调。在这些差异表达基因中，60个与转录调控相关，18个基因被注释为减数分裂相关基因。对使用携带双中性基因Saⁿ和Sbⁿ的同源四倍体水稻培育出的杂种进行分析，结果显示花粉育性正常，转录组分析表明不同杂种间差异表达基因的数量无显著差异。
我们的研究发现表明，Sa和Sb花粉不育位点的普遍互作导致同源四倍体杂种中出现高不育性，进而导致重要的减数分裂相关基因和转录调控因子下调。此外，我们还发现同源四倍体水稻杂种中的双中性基因Saⁿ和Sbⁿ可克服杂种不育性。本研究为同源四倍体水稻杂种中杂种优势的利用提供了有力证据。
