Matyasek R, Lim K Y, Kovarik A, Leitch A R
Institute of Biophysics, Academy of Sciences of the Czech Republic, CZ-61265 Brno, Czech Republic.
Heredity (Edinb). 2003 Sep;91(3):268-75. doi: 10.1038/sj.hdy.6800333.
Genomic in situ hybridisation was used to confirm that Nicotiana rustica (2n=4x=48) is an allotetraploid between N. paniculata (2n=2x=24, maternal P-genome donor) and N. undulata (2n=2x=24, paternal U-genome donor), their progenitors or species closely related to them. Fluorescent in situ hybridisation showed that N. paniculata has one 5S and two 18-5.8-26S rDNA loci whereas N. undulata has an additional 18-5.8-26S rDNA locus. N. rustica has the sum of the loci found in these putative parents. The sizes of the 18-5.8-26S rDNA loci indicate that the number of rDNA units on the U-genome chromosomes has amplified; perhaps this is associated with a concomitant reduction in the number of units on P-genome chromosomes. Restriction fragment length polymorphism analysis of the intergenic spacer (IGS) of the 18-5.8-26S rDNA units in N. rustica and the two progenitor diploids revealed that about 80% of IGS sequences in N. rustica are of an N. undulata type and 20% of N. paniculata type. These data indicate that interlocus sequence homogenisation has caused the replacement of many N. paniculata-type IGSs in N. rustica with an N. undulata-type of sequence. It is probable that subsequent to this replacement there has been sequence divergence at the 5' end of the IGS. As in tobacco, an allotetraploid between N. sylvestris and N. tomentosiformis, the direction of the IGS interlocus conversion is towards the paternal genome donor.
基因组原位杂交被用于证实黄花烟草（2n = 4x = 48）是圆锥烟草（2n = 2x = 24，母本P基因组供体）和波叶烟草（2n = 2x = 24，父本U基因组供体）、它们的祖先或与其密切相关的物种之间的异源四倍体。荧光原位杂交显示，圆锥烟草有一个5S和两个18 - 5.8 - 26S rDNA位点，而波叶烟草有一个额外的18 - 5.8 - 26S rDNA位点。黄花烟草具有这些假定亲本中发现的位点总和。18 - 5.8 - 26S rDNA位点的大小表明，U基因组染色体上rDNA单位的数量已经扩增；也许这与P基因组染色体上单位数量的相应减少有关。对黄花烟草以及两个二倍体祖先的18 - 5.8 - 26S rDNA单位的基因间隔区（IGS）进行限制性片段长度多态性分析，结果显示，黄花烟草中约80%的IGS序列是波叶烟草类型，并20%是圆锥烟草类型。这些数据表明，位点间序列均一化导致黄花烟草中许多圆锥烟草型IGS被波叶烟草型序列所取代。很可能在这种取代之后，IGS的5'端出现了序列分歧。如同烟草（一种森林烟草和绒毛状烟草之间的异源四倍体）一样，IGS位点间转换的方向是朝着父本基因组供体。
