BACKGROUND Neo-tetraploid rice, which is a new germplasm developed from autotetraploid rice, has a powerful biological and yield potential and could be used for commercial utilization. The length of panicle, as a part of rice panicle architecture, contributes greatly to high yield. However, little information about long panicle associated with heterosis or hybrid vigor is available in neo-tetraploid rice. RESULTS In the present study, we developed a neo-tetraploid rice line, Huaduo 8 (H8), with long panicles and harboring wide-compatibility genes for pollen and embryo sac fertility. All the hybrids generated by H8 produced significant high-parent yield heterosis and displayed long panicles similar to H8. RNA-seq analysis detected a total of 4013, 7050, 6787 and 6195 differentially expressed genes uniquely belonging to F1 and specifically (DEGFu-sp) associated with leaf, sheath, main panicle axis and spikelet in the two hybrids, respectively. Of these DEGFu-sp, 279 and 89 genes were involved in kinase and synthase, and 714 cloned genes, such as GW8, OsGA20ox1, Ghd8, GW6a, and LP1, were identified and validated by qRT-PCR. A total of 2925 known QTLs intervals, with an average of 1~100 genes per interval, were detected in both hybrids. Of these, 109 yield-related QTLs were associated with seven important traits in rice. Moreover, 1393 non-additive DEGs, including 766 up-regulated and 627 down-regulated, were detected in both hybrids. Importantly, eight up-regulated genes associated with panicle were detected in young panicles of the two hybrids compared to their parents by qRT-PCR. Re-sequencing analysis depicted that LP (a gene controlling long panicle) sequence of H8 was different from many other neo-tetraploid rice and most of the diploid and autotetraploid lines. The qRT-PCR results showed that LP was up-regulated in the hybrid compared to its parents at very young stage of panicle development. CONCLUSIONS These results suggested that H8 could overcome the intersubspecific autotetraploid hybrid rice sterility caused by embryo sac and pollen sterility loci. Notably, long panicles of H8 showed dominance phenomenon and played an important role in yield heterosis, which is a complex molecular mechanism. The neo-tetraploid rice is a useful germplasm to attain high yield of polyploid rice.

中文翻译：

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广泛兼容的长穗新四倍体水稻品系的杂种优势分析和潜在的分子调控机制。

背景技术新四倍体水稻是从同源四倍体水稻发展而来的新种质，具有强大的生物学和产量潜力，可用于商业用途。穗的长度，作为水稻穗结构的一部分，极大地促进了高产。但是，在新四倍体水稻中几乎没有关于与杂种优势或杂种优势相关的长穗的信息。结果在本研究中，我们开发了一种新的四倍体水稻系华多8号（H8），穗长且具有广泛的花粉和胚囊育性兼容基因。H8产生的所有杂种均产生显着的高亲本产量杂种优势，并显示出与H8相似的长穗。RNA-seq分析共检测到4013、7050，6787和6195差异表达的基因分别独特地属于F1，特别是与两个杂种中的叶，鞘，主穗轴和小穗相关的（DEGFu-sp）。在这些DEGFu-sp中，有279个基因和89个基因参与了激酶和合酶，并通过qRT-PCR鉴定并验证了714个克隆基因，例如GW8，OsGA20ox1，Ghd8，GW6a和LP1。在两个杂种中共检测到2925个已知QTL间隔，每个间隔平均1〜100个基因。其中109个与产量相关的QTL与水稻的七个重要性状有关。此外，在两个杂种中均检测到1393个非加性DEG，包括766个上调和627个下调。重要的是，通过qRT-PCR，与它们的亲本相比，在两个杂种的幼穗中检测到与穗相关的八个上调基因。重新测序分析表明，H8的LP（控制长穗的基因）序列与许多其他新四倍体水稻以及大多数二倍体和同源四倍体系不同。qRT-PCR结果表明，在幼穗发育很早的阶段，与亲本相比，杂种中的LP上调。结论这些结果表明，H8可以克服由胚囊和花粉不育位点引起的亚种间四倍体杂交水稻不育。值得注意的是，H8长穗显示出优势现象，并且在产量杂种优势中起重要作用，这是一个复杂的分子机制。新四倍体水稻是获得高产多倍体水稻的有用种质。