【作者】 刘三宏；

【导师】 王坤波； 宋国立；

【作者基本信息】 中国农业科学院 ， 作物遗传育种， 2004， 硕士

【摘要】 多倍体的形成在生物进化过程中占有重要的地位，但是我们对其多倍化后基因组究竟发生了哪些变化还知之甚少。棉属（Gossypium）比较适合于基因组起源与演化的研究，它共约有51个种，分为9个基因组类型。先前的研究已表明，四倍体棉种（AD）是异源多倍体，它包含A基因组和D基因组。随着研究手段的创新，在四倍体棉种起源、演化和分类等重大基本理论上已基本形成共识。但是，四倍体棉种的具体供体种及其起源过程的种质歧化、棉属染色体组之间或组内各棉种的同源程度等仍有分歧。 本研究使用FISH方法对此进行初步探讨，主要包括：四倍体棉种供体种研究、四倍体棉种多元进化和单元进化的研究以及rDNA同步进化的研究。研究结果如下： 1．以四倍体棉种A基因组可能的供体种阿非利加棉、亚洲棉的gDNA（genomic DNA）及其D基因组可能的供体种雷蒙德氏棉、瑟伯氏棉、戴维逊氏棉、拟似棉的gDNA为探针，分别与四倍体棉种的体细胞（SC）和花粉母细胞（PMC）进行FISH实验。在以A基因组二倍体棉种gDNA为探针的实验中，发现A基因组的一些重复序列入侵到D基因组上，并且A基因组与四倍体A基因组的关系要比D基因组与四倍体D基因组的关系近。在以D基因组二倍体棉种gDNA为探针的实验中，发现戴维逊氏棉与陆地棉D基因组的关系最近，雷蒙德氏棉与海岛棉D基因组的关系最近，从而推测四倍体棉种是多系起源而不是单系起源的。并发现拟氏棉是D基因组棉种中一个特殊的种。 2．在（AD）₁×A_1-a组合中，从二价体多，偶尔也有AAA三价体和AAAA四价体出现，说明阿非利加棉染色体(A_1-a)与陆地棉的A组染色体尽管基本上相同，但还是存在着差别。在（AD）₂×D₁和（AD）₂×D₅组合中，DD二价体出现的频率基本上一样，但从信号显示的情况看，雷蒙德氏棉比瑟伯氏棉与海岛棉D基因组的关系近。 3．以45S rDNA为探针，分别以陆地棉、海岛棉、黄褐棉为靶DNA进行FISH实验，发现陆地棉和海岛棉的45S rDNA全部同步进化为D基因组类型的rDNA；而黄褐棉的45S rDNA全部同步进化为A基因组类型的rDNA。这说明在四倍体中，45S rDNA的同步进化是双向的。并且在四倍体中，45S rDNA全部位于染色体短臂的端部，从而推测二倍体棉种的45S rDNA在多倍体中像转座子一样能够在染色体上移动。更多还原

【Abstract】 Polyploid formation has played a major role in the evolution of many plant and animal genomes, however, surprisingly little is known for us what happens to genomes in polyploidy. The genus Gossypium is a facile system for investigating the genomic organization and evolution. Gossypium includes about 51 species, grouped into 9 genome types. It has been proposed previously that extant A-and D-genome species are most closely related to the diploid progenitors of the tetraploid(A.D genome). Powerful new technologies have been begun to be brought to bear on the problem of the origin and evolution of tetraploid cotton, some investigators has gotten some same conclusions. Yet few data address the question of the actual diploid ancestor of tetraploid D-subgenome, the relationship between the diploid genome and tetraploid genome, and some diploids’ homologous relationship, et al. Some research results are different from each other.Fluorescent in situ hybridization (FISH) is used to explore the origin and evolution of tetraploid cotton in this study. The contents include the diploid ancestors of tetraploid cotton, polyphyletic or monophyletic origin of tetraploid cotton, and rDNA concerted evolution. The main results are as follows:1.In this study, gDNA(genomic DNA) of A-genome diploid cotton G.herbaceum var.africanum and Garboreum and gDNA of the D-genome diploid cotton Graimondii, G.davidsonii, Gthurberi, Ggossypiodies are used as probe, respectively. The somatic cell and pollen mother cell of tetraploid cotton are used as target DNA, respectively. The results of A-genome diploid cotton gDNA as probe show that some A-genome dispersed repetitive sequences have "invaded" D-genome. The phenomenon that the A-genome of allopolyploid cotton is more similar to that of the A-genome diploids than the D-genome of the allopolyploid is to that of the D-genome diploids can be also observed in this study. Moreover, the results of D-genome diploid cotton gDNA as probe show that Gdavidsonii is the proposed D-genome progenitor of Ghirsutum, and Graimondii is the proposed D-genome progenitor of Gbarbadense. This result maybe implicate that tetraploid cotton are polyphyletic origin. Furthermore, Ggossypiodies is very special and different with other D-genome diploid cotton from FISH images demonstration.2.Signals in the hybrid of (AD) 1×A1-a show that more AA bivalent, sometimes AAA trivalent and AAAA tetravalent. This suggests that there are some differences between Gherbaceum var.africanum genome and Ghirsutum A-subgenome although they are almost same. Signals in the hybrid (AD) 2×D1 and (AD) 2×D5, the frequency of DD bivalent in two hybrids is almost same but Graimondii genome and Gbarbadense D-subgenome are more homologous than Gthurberi from the intensity of shown signals.3.In this study, 45S rDNA was used as probe hybridized with Ghirsutum, Gbarbadense, G.mustelinum as target DNA, respectively. In the results, rDNA of Ghirsutum, Gbarbadense havebeen homogenized to D genome repeat type, whereas rDNA of Gmustelinum have concerted to A genome repeat type. This phenomenon shows that interlocus concerted evolution can occur bidirectionally subsequent to hybridization and polyploidization. And all of the 45S major loci in tetraploid cotton were located on the terminal end of the short arms of chromosomes. These results implicate that 45 S rDNA can move from one region to another regions on one chromosome or from one chromosome to another chromosomes just like transponsons.更多还原