【作者】 马谦；

【导师】 张启发；

【作者基本信息】 华中农业大学 ， 生物化学与分子生物学， 2011， 博士

【摘要】 水稻(Oryza sativa L.)是世界上最重要的粮食作物之一。利用杂种优势提高水稻产量,是保证世界粮食安全的一条有效途径。要想全面认识和了解杂种优势这一现象的生物学基础,就需要从遗传水平、分子水平和生理水平来进行全面的分析和研究。在水稻中,尽管已经开展了许多关于杂种优势的研究,并且这些研究结果也的确加深了我们对于杂种优势的遗传基础和分子基础的认识,但是关于杂种优势生理学基础的研究却鲜有报道。植物激素在生理水平上,对植物的生长和发育发挥着及其重要的调控作用。并且已有研究认为,赤霉素(GAs)在杂种优势形成的植物激素调控过程中发挥着重要的基础作用。本研究的目的,就是为了更加深入的调查赤霉素在水稻苗期杂种优势形成过程中所发挥的生理调控作用,从而为揭示植物激素是水稻杂种优势的生理学基础提供证据。为此,我们使用生产上具有代表性的3个保持系(做母本)和3个恢复系(做父本),通过系间相互杂交,构建了一个包含9种杂交组合的不完全双列杂交组合(3×3incomplete diallel set)。首先,我们的苗期性状调查结果显示,在幼苗干重(SDW)、幼芽干重(ADW)和幼苗分蘖数(TN)这三个性状上存在着显著但是不同程度的杂种优势。干重和分蘖数的中亲优势率的变化范围分别为-9%—61.7%和1.4%—73.3%；幼芽干重的中亲优势率的变化范围是3.7%—64.4%。接着,我们使用GC-MS技术,对这套材料的20DAS幼苗和4d幼芽中,内源赤霉素的含量进行了精确分析。值得一提的是,本研究对GA代谢途径上的各种GAs分子——不仅仅包括活性GAs,还包括其前体物和代谢产物,均进行了精确定量。而这体现了本研究的一大特色：第一个在植物杂种优势分析中对尽可能多的赤霉素分子种类进行了如此全面的定量分析。20DAS幼苗中,赤霉素含量的杂种优势程度不高,在杂种中以亲本的加性效应为主；而4d幼芽中GA含量优势明显。然后,我们还使用实时荧光定量RT-PCR技术,对20DAS幼苗中GA代谢和信号传导基因的表达模式进行了准确分析。十分有趣的是：在16个基因中有13个基因(占81%)表现出差异性表达(differential expression);在出现差异性表达的情况中绝大部分(95%)表现为非加性作用模式(nonadditive modes of gene action),尤其以正向超显性(overdominance)和正向显性(positive dominance)模式为主。在此基础上,我们将上述实验数据综合起来进行了相关分析,结果发现：一些GA分子的含量与幼苗干重和分蘖数的杂种优势间存在显著的相关性；与此相呼应的是,一些GA相关基因的表达量与幼苗干重和分蘖数的杂种优势间也检测到了显著的相关性。本研究所得到的这些结果表明：赤霉素从生理水平上,对水稻苗期杂种优势的形成起着重要的调控作用。更多还原

【Abstract】 Rice(Oryza sativa L.) is one of the most important food crops in the world. To solve the problem of the world food security, heterosis can be exploited to improve the yield potential of rice. A comprehensive understanding of the biological mechanism for heterosis will definitely benefit from knowledge at three levels:genetic, molecular and physiological. In rice, although many studies have been performed to contribute to a better understanding of the genetic and molecular basis of heterosis, little efforts have been made towards the physiological basis. Plant hormones play a vital role in the physiological regulation of plant growth and development, and it was proposed that gibberellins (GAs) provide a phytohormone basis for heterosis in plant. The study presented here is designed to investigate in depth the physiological role of GAs in the regulation of heterosis for rice seedling growth, or the hormonal basis for heterosis of rice.For this purpose, we developed a3×3incomplete diallel set and a matrix of all possible single-cross hybrids between them. Substantial and varying degree of heterosis for seedling growth was observed on the traits of SDW, ADW and TN. Mid-parent heterosis (MPH) ranged from-9%to61.7%for shoot dry weight,1.4%to73.3%for tiller number and3.7%to64.4%for axes dry weight.Then, the endogenous levels of GAs in these rice strains were measured unequivocally for the growing shoots of20DAS seedlings and the shoot plus root axes of4-d-old germinating seeds by GC-MS. It is worthy to note that all the molecules along the GA metabolic pathway, including not only bioactive GAs but also their precursors and catabolites, are included in the quantification analysis. To our knowledge, this might be the first study having such a full coverage of GA molecule species for heterosis analysis in plant. For20DAS seedlings, heterosis of GA contents was low and the contents in the hybrids were close to the means of the parents. In the shoot plus root axes of4-d-old germinating seeds, heterosis was relatively high.Furthermore, we also examined the expression profiles of a wide range of GA metabolism and signaling genes in rice using real time RT-PCR for the growing shoots of rice seedlings at20DAS. The cases of differential expression were frequently detected for most of the genes examined (13out of16), in the majority of which nonadditive modes of gene action were found, predominantly as the modes of overdominance and positive dominance.Through the combinative correlation analyses of the above data, we observed highly significant correlations of the contents of certain GA species with performance and heterosis of shoot dry mass and also with heterosis of tillering number. In accordance with this, strong correlations were detected between expression levels of certain GA-related genes and heterosis for shoot dry weight and tillering number, and also between heterotic expression effects of certain genes with heterosis of shoot dry weight. These strong correlations imply that GAs may play an important role at the physiologcial level in the regulation of heterosis for rice seedling growth.更多还原