【作者】 万东石；

【导师】 刘建全；

【作者基本信息】 兰州大学 ， 生态学， 2010， 博士

【摘要】 基因重复为植物应对环境胁迫机制的更新进化提供了丰富的遗传原材料,是植物进化的根本动力。植物通过基因重复,以及重复拷贝之间的表达分化,不仅为植物分化产生重要的生物功能,也为植物产生高度分化的适应性性状提供分子遗传基础。本研究选择经过快速辐射进化成种的典型代表、主要分布在青藏高原的大黄属物种作为研究对象,研究该类群中抗逆相关基因-类黄酮代谢途径的关键酶-查尔酮合成酶编码基因CHS类基因的进化式样。主要结果如下：(1)使用克隆方法,在16个大黄属物种以及8个相关属物种中克隆获得了36条CHS类基因序列。系统发育分析表明,大黄属及其它属形成了明显的属特异性分支；大黄属类群没有形成种特异性的结构关系,而是属内物种聚在一起,来自于同一个祖先分支的两个拷贝分别聚类为明显的两大分支,分别为A分支和B分支,表明大黄属类群在其物种起源后,发生了一次快速、独立的基因重复事件；来自两种大黄(苞叶大黄和塔黄)基因组DNA的Gel bloting结果进一步证实了大黄属CHS-like发生了一次基因重复事件,基因组中CHS重复基因至少有2个拷贝。(2)大黄属两个CHS基因拷贝CHSA和CHSB的同义替代率没有显著差别,而非同义替换率差异显著,重复基因CHSB有更高的非同义替换率,表明两者在进化选择上受到的约束明显不同；CHSB分支的ω是CHSA分支的3倍,likelihood分析结果也进一步表明两个分支之间差异显著。这些结果表明,大黄属B分支在经过基因重复后,非同义替代率显著增加,受到的选择压力显著高于A分支。同时,应用分支-位点模型,发现大黄CHSB分支编码氨基酸的一个位点受到了强烈的正选择(后验概率p=0.997)(3)大黄属CHS基因exon2 DNA片段构建的系统发育关系中,大黄属种间遗传分化小,多呈平行分支,系统树反应的大黄属发育系统关系和基于叶绿体基因片段构建的系统进化关系基本相似,显示出典型的物种快速辐射多样化特征。更多还原

【Abstract】 Gene duplication provides raw materials for further innovative evolution in plants in response to various stressful environments and natural selection. In this study, we aimed to examine evolutionary history of the CHS-like genes in the Rheum, a genus with a radiative history with its most species occurring mainly in the Qinghai-Tibetan Plateau. The main results and conclusions are listed as following,(1)A total of 36 CHS-like sequences were obtained through sequencing the clones of the PCR CHS amplification of 16 Rheum species and eight ones from the other closely related genera. Phylogenetic analyses of these sequences suggested that all CHS-like sequences from Rheum comprised a monophyletic lineage and within the genus, two subclades with high supports were recovered. These analyses indicated that since origin of the genus Rheum, CHS had undergone an independent duplication. DNA Gel blotting analyses further confirmed this suggestion that at least two CHS-like members are present in two species.(2) Based on the branch-model, the ratio of the non-synonymous and synonymous substitutions within the subclades A (ω1=0.1454) and B (ω2=0.4532) ratios were significantly different from each other and also the background ratioω0 (0.0222). It is suggested that an increase in the nonsynonymous substitution rate occurred in the lineage ancestral to CHSB after gene duplication. Branch-site model analyses also indicated that one site (G243) within the CHSB was driven significantly by positive selection with the posterior probability (P=0.997).(3) Within each subclade, the relationships between different species were rarely recovered and the pattern is a typical "paralleling" phylogeny, suggesting a radiative diversificiation. This result is consistent with the previous phylogenetic analysis based on the chloroplast DNA sequences.更多还原