杨柳分化及其性别决定的基因组学基础

发布时间：2018-05-08 01:02

本文选题：染色体重排 + 物种分化　；参考：《南京林业大学》2016年博士论文

【摘要】：杨属和柳属是杨柳科的姐妹属,一般以二倍体形式存在。以前基因组的研究表明杨属和柳属起源于同一个古四倍体祖先。在本研究中,我们首次对簸箕柳的染色体进行了组装。在染色体的水平上,分别对毛果杨和簸箕柳进行基因组内的比较分析,结果显示在两个基因组中,每条染色体在基因组的其它位置上都有同源片段的存在,而且同源片段的分布情况非常相似,这一结果不仅证实了同一起源的说法,还表明两个物种的分化发生在古四倍体祖先重新二倍化之后。除此之外,1号和16号染色体同源片段的分布在两个基因组间差异较大。经过杨树和柳树基因组间的比较分析,发现在1号和16号染色体间出现了两个大的染色体重排。杨树1号染色体的上半部分与柳树的16号染色体同源,而杨树的16号染色体与柳树的1号染色体的上半部分同源。这说明在杨树和柳树这两个物种形成过程中,1号和16号染色体间发生了断裂融合。以前通过杨、柳形态学上的研究认为杨树较柳树原始,柳树是由杨树进化形成的。在此基础上,我们提出了杨柳科植物进化的模型:杨柳科植物的祖先基因组在距今约5,800万年前发生了一次杨柳科植物特有的全基因组复制事件(“salicoid”duplication)。全基因组复制以后,古四倍体基因组又发生了染色体的断裂与融合,基因组进行了重新二倍化,首先形成了现代杨树的祖先。在随后的进化过程中,杨树的1号染色体发生了着丝粒断裂,其下半部分与16号染色体的端粒进行融合形成了柳树的1号染色体,而其上半部分进化形成了柳树的16号染色体。经过这一染色体重排事件,诞生了现代柳树的祖先。本研究为揭示高等植物在全基因组复制之后近缘物种的分化机制的研究奠定了基础。另外,杨属和柳属是雌雄异株植物,是研究植物性染色体进化的理想材料。以前的研究证明:在杨属中,19号染色体进化成了性染色体。而本研究通过对性别基因的定位发现柳属植物的性染色体是由15号染色体进化形成的。杨属植物中存在ZZ/ZW和XX/XY两种性别决定系统。而柳属中的簸箕柳的性别决定系统为ZZ/ZW,在雌性个体有2条不同的性染色体。将毛果杨的15号常染色体和19号性染色体分别与簸箕柳的15号性染色体和19号常染色体进行共线性分析,结果显示杨树的19号性染色体与柳树的19号常染色体同源,柳树的15号性染色体与杨树的15号常染色体同源,并且柳树的两条性染色体出现了染色体重排,而杨树的19号性染色体与柳树的15号性染色体间没有同源性。由于柳树和杨树起源于同一个祖先进化而来的,因此,我们推测杨、柳性染色体的形成发生在物种分化之后,是由不同的常染色体进化而来的。本研究揭示了杨柳性染色体的进化机制,为雌雄异株植物性染色体的进化研究奠定了基础。
[Abstract]:Poplar and willow are sister genera of willow family, which generally exist in diploid form. Previous genome studies have shown that poplar and willow originated from the same paleotetraploid ancestor. In this study, we assembled the chromosome of dustpan willow for the first time. At the chromosome level, a comparative analysis of the genome of Populus tomentosa and Willow dustpan was carried out. The results showed that homologous fragments were found in each chromosome in the other parts of the genome. The distribution of the homologous fragments was very similar, which not only confirmed the same origin, but also indicated that the differentiation of the two species occurred after the paleotetraploid ancestors redoubled. In addition, the distribution of homologous fragments on chromosome 1 and 16 differed greatly between the two genomes. Through the comparative analysis of the genomes of poplar and willow, it was found that there were two large chromosome rearrangements between chromosome 1 and chromosome 16. The upper part of poplar chromosome 1 is homologous to chromosome 16 of willow, while chromosome 16 of poplar is homologous to the upper part of chromosome 1 of willow. This indicates that the breakage and fusion occurred between chromosome 1 and chromosome 16 during the formation of poplar and willow. It is considered that poplar is more primitive than willow, and willow is formed by poplar evolution through morphological study of poplar and willow. On the basis of this, we put forward a model of the evolution of the family willow. The ancestral genome of the family willow occurred about 5800 years ago, a "salicoid" replication-specific event occurred in the whole genome of the family Salicaceae. After the whole genome was duplicated, the paleotetraploid genome was broken and fused again, and the genome was redoubled. First, the ancestor of modern poplar was formed. In the course of subsequent evolution, the metacentric cleavage occurred on chromosome 1 of poplar, and the lower part of it fused with the telomere of chromosome 16 to form chromosome 1 of willow, while the upper part of it evolved to form chromosome 16 of willow. Through this chromosome rearrangement event, the ancestor of modern willow was born. This study laid a foundation for the study of the differentiation mechanism of relative species in higher plants after genome replication. In addition, Poplar and Willow are dioecious plants, which are ideal materials for studying the evolution of sexual chromosomes in plants. Previous studies have shown that chromosome 19 evolved into a sex chromosome in poplar. In this study, it was found that the sex chromosomes of willow plants were evolved from chromosome 15. There are two sex determination systems, ZZ/ZW and XX/XY, in poplar plants. The sex-determining system of willow is ZZ / ZW, which has two different sex chromosomes in female individuals. The co-linear analysis of autosomal chromosome 15 and sex chromosome 19 of Populus tomentosa was carried out, respectively. The results showed that the sex chromosome 19 of poplar was homologous to autosomal 19 of willow. The sex chromosome 15 of willow is homologous to autosomal 15 of poplar, and the two sex chromosomes of willow have chromosome rearrangement, but there is no homology between sex chromosome 19 of poplar and sex chromosome 15 of willow. Since willow and poplar originated from the same ancestor, we speculate that the formation of poplar and willow chromosomes occurred after species differentiation and evolved from different autosomes. This study revealed the evolutionary mechanism of willow sex chromosomes and laid a foundation for the study of the evolution of sexual chromosomes in dioecious plants.
【学位授予单位】：南京林业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S718.4

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