Zhu Dan, Zhou Gang, Xu Caiguo, Zhang Qifa
National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan 430070, China.
National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan 430070, China.
J Genet Genomics. 2016 Feb 20;43(2):87-97. doi: 10.1016/j.jgg.2016.01.002. Epub 2016 Jan 20.
Utilization of heterosis has greatly contributed to rice productivity in China and many Asian countries. Superior hybrids usually show heterosis at two stages: canopy development at vegetative stage and panicle development at reproductive stage resulting in heterosis in yield. Although the genetic basis of heterosis in rice has been extensively investigated, all the previous studies focused on yield traits at maturity stage. In this study, we analyzed the genetic basis of heterosis at seedling stage making use of an "immortalized F2" population composed of 105 hybrids produced by intercrossing recombinant inbred lines (RILs) from a cross between Zhenshan 97 and Minghui 63, the parents of Shanyou 63, which is an elite hybrid widely grown in China. Eight seedling traits, seedling height, tiller number, leaf number, root number, maximum root length, root dry weight, shoot dry weight and total dry weight, were investigated using hydroponic culture. We analyzed single-locus and digenic genetic effects at the whole genome level using an ultrahigh-density SNP bin map obtained by population re-sequencing. The analysis revealed large numbers of heterotic effects for seedling traits including dominance, overdominance and digenic dominance (epistasis) in both positive and negative directions. Overdominance effects were prevalent for all the traits, and digenic dominance effects also accounted for a large portion of the genetic effects. The results suggested that cumulative small advantages of the single-locus effects and two-locus interactions, most of which could not be detected statistically, could explain the genetic basis of seedling heterosis of the F1 hybrid.
杂种优势的利用对中国和许多亚洲国家的水稻产量提高做出了巨大贡献。优良杂交种通常在两个阶段表现出杂种优势：营养生长期的冠层发育和生殖生长期的穗发育，从而导致产量杂种优势。尽管水稻杂种优势的遗传基础已得到广泛研究，但以往所有研究都集中在成熟期的产量性状上。在本研究中，我们利用一个“永久F2”群体分析了苗期杂种优势的遗传基础，该群体由105个杂交种组成，这些杂交种是由珍汕97和明恢63杂交产生的重组自交系（RIL）相互杂交而成，珍汕97和明恢63是汕优63的亲本，汕优63是在中国广泛种植的一个优良杂交种。通过水培法研究了8个苗期性状，即苗高、分蘖数、叶片数、根数、最大根长、根干重、地上部干重和总干重。我们使用通过群体重测序获得的超高密度SNP bin图谱，在全基因组水平上分析了单基因座和双基因座的遗传效应。分析揭示了苗期性状大量的杂种优势效应，包括正向和负向的显性、超显性和双基因显性（上位性）。所有性状中超显性效应普遍存在，双基因显性效应也占遗传效应的很大一部分。结果表明，单基因座效应和双基因座互作的累积小优势，其中大部分在统计学上无法检测到，可能解释了F1杂交种苗期杂种优势的遗传基础。
