Krishnan P, Sapra V T, Soliman K M, Zipf A
Department of Plant and Soil Science, Alabama A&M University, 4900 Meridian St., Carver Complex South, Room 213, Normal, AL 35762, USA.
J Hered. 2001 May-Jun;92(3):295-300. doi: 10.1093/jhered/92.3.295.
Wild germplasms are often the only significant sources of useful traits for crops, such as soybean, that have limited genetic variability. Before these germplasms can be effectively manipulated they must be characterized at the cytological and molecular levels. Modern soybean probably arose through an ancient allotetraploid event and subsequent diploidization of the genome. However, wild Glycine species have not been intensively investigated for this ancient polyploidy. In this article we determined the number of both the 5S and 18S-28S rDNA sequences in various members of the genus Glycine using FISH. Our results distinctly establish the loss of a 5S rDNA locus from the "diploid" (2n = 40) species and the loss of two from the (2n = 80) polyploids of GLYCINE: A similar diploidization of the 18S-28S rDNA gene family has occurred in G. canescens, G. clandestina, G. soja, and G. max (L.) Merr. (2n = 40). Although of different genome types, G. tabacina and G. tomentella (2n = 80) both showed two major 18S-28S rDNA loci per haploid genome, in contrast to the four loci that would be expected in chromosomes that have undergone two doubling events in their evolutionary history. It is evident that the evolution of the subgenus Glycine is more complex than that represented in a simple diploid-doubled to tetraploid model.
野生种质通常是大豆等遗传变异性有限的作物中有用性状的唯一重要来源。在有效利用这些种质之前，必须在细胞学和分子水平上对其进行表征。现代大豆可能起源于古代的异源四倍体事件以及随后的基因组二倍体化。然而，对于这种古老的多倍体现象，野生大豆属物种尚未得到深入研究。在本文中，我们使用荧光原位杂交技术确定了大豆属不同成员中5S和18S - 28S rDNA序列的数量。我们的结果清楚地表明，“二倍体”（2n = 40）物种中一个5S rDNA位点的丢失，以及大豆属（2n = 80）多倍体中两个5S rDNA位点的丢失：在灰毛豆、隐蔽豆、野生大豆和栽培大豆（2n = 40）中，18S - 28S rDNA基因家族也发生了类似的二倍体化。尽管基因组类型不同，但烟草状大豆和绒毛大豆（2n = 80）每个单倍体基因组均显示出两个主要的18S - 28S rDNA位点，这与在进化历史中经历了两次加倍事件的染色体中预期的四个位点形成对比。显然，大豆亚属的进化比简单的二倍体加倍形成四倍体模型所呈现的更为复杂。
