基于CSSSLs群体的水稻杂种优势机理的解析和功能基因鉴定

Heterosis is a universal biological phenomenon in which the hybrids exhibit superior agronomic performance than either inbred parental lines. Hybrid rice has made a tremendous contribution to food security both in China and other countries.Recently tens of super rice varieties have been bred by the combination of heterosis with ideotype in China. Although there have been great achievements in hybrid rice breeding ,the yield potential of hybrid rice has apparently reached a plateau in the last twenty years. Elucidation of the genetic mechanisms underlying heterosis and characterization of genes (or QTLs) associated with heterosis provides an opportunity to break the ceiling of yield potential. Despite heterosis is used extensively in agriculture, the genetic basis of which has been debated for almost one century, especially the molecular mechanisms underlying heterosis remain elusive, since it is complex, the additive effect , dominant effect ,overdominant effect and epistasis all play important roles in the performance of heterosis. Breeding of the advanced genetic populations is the first and most important work to finely locate the loci related to heterosis and estimate the genetic effect of these loci on heterosis..In our previous research works, a set of rice chromosome single segment substitution lines (CSSSLs) have been bred for the characterization of genes associated with heterosis with 9311 as the recurrent parent with molecular marker-assisted selection (MAS),since 9311 is the male parent of several hybrid rice varieties with the biggest cultivated area. The size and precise position of each introduced segment in every line of this population was identified with the high- resolution single nucleotide polymorphic (SNP) markers developed by resequencing with the next-generation sequencing techniques.In this proposal,testcross and diallel cross populations are planned to be made to precisely estimated the additive effect ,dominant effect ,overdominant effect and epistasis on the heterosis based on this CSSSLs population . Map-based cloning strategy will be used to finely map and clone the genes related to heterosis with the development of the advanced introgression and testcross populations and expression profile analysis will be carried out simultaneously.The function of the candidate genes related to heterosis will be validated by the performance of transgenic lines of complementary，RNAi and overexpression of the target genes. The elite lines by pyramiding of the favorable alleles related to heterosis will be selected for hybrid rice breeding with marker-assisted selection.After the completion of the project,the additive effect,dominant effect,overdominant effect and epistasis on heterosis will be clearly elucidated. The genes related to heterosis will be fine located and two of them will be cloned and characterized.Several hybrid rice lines will be bred and evaluated in the regional trials.About 5 SCI papers will be published.

水稻是我国最重要的粮食作物之一。水稻的高产和稳产对于保障我国的粮食安全具有重要作用。超级杂交稻育种是水稻改良的有效途径之一，而水稻杂种优势形成机理研究则是培育超级杂交稻的基础并有助于加深人们对作物杂种优势形成机理的认识。本研究组在前期工作中,培育了以强优杂交稻组合的亲本9311为遗传背景的水稻单片段代换系群体，通过重测序分析了每个株系导入片段的大小和位置,并开展了杂种优势机理的初步研究。本项目拟利用这套水稻单片段代换系群体为基础群体,通过测交、双列杂交构建杂种优势分析群体，分析不同遗传效应对杂种优势的贡献率；通过回交和分子标记分析，构建杂种优势相关基因或调控因子的渐渗系群体，利用图位克隆方法结合转录组学等研究分离杂种优势相关基因或调控因子；通过杂种优势相关基因或调控因子的功能分析结合转录组学研究，阐明作物杂种优势形成的机理和遗传网络；利用所获得的材料和基因资源，开展杂交水稻分子育种研究。

水稻杂种优势遗传机理还知之甚少。为此，我们利用一套重测序的128个水稻染色体片段代换系分别和水稻光温敏雄性核不育系广占63-4s、036S和连99S杂交，构建了4套测交系群体，分别命名为TC1-TC4（TC1为广占63-4s×CSSLs，2009年；TC2为广占63-4s×CSSLs，2011年；TC3为036S×CSSLs，2015年；TC4为连99S×CSSLs，2015年），进行性状考察，结合染色体片段代换系的分子信息，对水稻杂种优势遗传机制展开研究，并得到了如下的结果：.1、在TC 1中，除了结实率和千粒重之外，其余性状均值都高于CSSLs的均值；2011年TC 2群体中，穗长、单株有效穗数和单株产量的均值表现要优于CSSLs的均值表现；TC 3与CSSLs的7个性状均值比较发现，TC 3的穗长和单株有效穗数平均值高于CSSLs的平均值；TC 4的穗长、单株有效穗数、穗粒数和单株产量的均值都高于CSSLs。以上结果表明不同的不育系一般配合力不同，而广占63-4s和连99s一般配合力较高。.2、我们对CSSLs与4个TCs的7个相对性状进行相关性分析，除了单株有效穗数和结实率之外，其余性状在CSSLs和TCs之间存在较高的相关性，因此选择优良的恢复系对于培育优良杂交组合至关重要。.3、根据128个染色体片段代换系及受体亲本9311的性状表型值，结合Bin-map，基于多元回归分析方法，在2009年、2011年和2015共定位到62个产量相关性状QTLs，根据测交系及对照组合的性状表型值，计算杂种优势值，共定位到97个杂种优势相关位点，这些杂种优势位点都被准确的定位在染色体的具体区段上，且检测到4个杂种优势位点簇。.4、对测交系各个表型值进行了方差分析。结果表明，株高、穗长、单株产量和千粒重的广义遗传率较高分别是79.85%，51.22%，76.75%和75.50%，均超过了50%。表明在杂种中，这些性状的变异，遗传的作用是主要的。单株穗数的广义遗传率最低，为21.47%，表明该性状极易受环境的影响。株高、穗长、结实率、单株产量和千粒重这5个性状表现为部分显性，每穗粒数表现为超显性。.本项目的研究结果初步解析了两系法杂交籼稻杂种优势可能的遗传模式，为开展水稻杂种优势的分子标记辅助选择育种提供了重要分子信息。

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