二倍体野生棉与四倍体栽培棉基于GISH的遗传关系分析

目的]研究二倍体野生棉与四倍体栽培棉间的遗传亲缘关系,进一步探索各棉种间的起源与进化.方法]以5个二倍体基因组的代表种B1(异常棉)、C1(斯特提棉)、E2(索马里棉)、F1(长萼棉)以及G1(比克氏棉)的基因组DNA(gDNA)为探针,以2个四倍体栽培种(陆地棉中棉所16、海岛棉新海7号)有丝分裂中期染色体为靶DNA,进行了基因组原位杂交(Genomic in situ hybridization,GISH)分析.结果]以B1、E2和F1gDNA为探针时,杂交信号主要分布在2个栽培种较长的13对A亚组染色体上;各产生3对较强的GISH-NOR信号,其中1对分布在较长的A亚组上,2对分布在较短的D亚组上,其GISH-NOR信号强度与分布情况与以D基因组棉种为探针时相似.说明二倍体B、E、F基因组与四倍体棉A亚基因组具有较高的同源性,亲缘关系更近.这一点与它们的地理分布情况相符;而它们基因组中的45S rDNA重复序列与二倍体D基因组的45SrDNA重复序列同源性较高.C1和G1中以gDNA为探针时,杂交信号分布在2个栽培种全部26对染色体上,无法区分开A或D亚组染色体,都有3对较强的GISH-NOR信号.这一现象与D基因组拟似棉(D6) gDNA为探针的GISH相似,表明二倍体C和G基因组与四倍体棉的A和D亚基因组均具有较高的同源性,或者C和G基因组同时含有A基因组(或其他非洲棉基因组)和D基因组成分,进一步证实了其基因组成分的杂合性;而它们基因组中的45S rDNA重复序列同属D基因组类型.结论]这些发现可为棉花杂交育种和棉属起源与演化研究提供有用信息.

Genomic in situ Hybridization Analysis of the Genetic Relationship between Wild-Type Diploid and Cultivated Allotetraploid Gossypium Species

Objective] This study investigated the genetic relationship between wild-type diploid and cultivated allotetraploid cotton species, and explored the origin and evolution of each species. Method] Genomic in situ hybridization (GISH) was performed on chromosomes of Gossypium hirsutum var. CCRI 16 and G. barbadense var. Xinhai 7 as representative species of wild-type diploid cotton B, E, and F genome species using G. anomalum, G. somalense, and G. longicalyx genomic DNA as probes. Results] The fluorescent signals were mainly distributed on A sub-genome chromosomes and were accompanied by three pairs of strong GISH-nucleolar organizer regions (NORs), one pair on the A sub-genome chromosomes and two pairs on the D sub-genome chromosomes. GISH-NOR signal intensities and distribution were similar for all diploid D genome gDNA probes. These results indicate that the G. anomalum, G. somalense, and G. longicalyx genome species have a closer genetic relationship with the tetraploid A sub-genome, which is consistent with their geographic distribution, while their 45S rDNA repeat sequences show higher homology with those of the D genome. Using G. sturtianum (C1) and G. bickii (G₁) gDNA as probes, fluorescent signals were distributed on all 26 pairs of chromosomes, the A and D sub-genomes were unable to be discriminated. This phenomenon was also observed using the D₆ genome species as a probe when three pairs of strong GISH-NOR signals were also detected. These findings suggest that the C and G genomes are highly homologous with the A and D sub-genomes of allotetraploid cotton species, or that they both contain A and D genome components leading to genome heterozygosity. However, their 45S rDNA repeat sequences appear to belong to the D genome type. Conclusion] These findings provide useful information for cotton hybrid breeding and researches on the origin and evolution of Gossypium species.