通过分子细胞遗传学分析评估的木本苜蓿属物种（Dendrotelis组）之间的关系。
Relationships of the woody Medicago species (section Dendrotelis) assessed by molecular cytogenetic analyses.
作者信息
Rosato Marcela, Castro Mercedes, Rosselló Josep A
机构信息
Jardí Botànic, Universidad de Valencia, c/Quart 80, E-46008 Valencia, Spain.
出版信息
Ann Bot. 2008 Jul;102(1):15-22. doi: 10.1093/aob/mcn055. Epub 2008 Apr 15.
BACKGROUND AND AIMS
The organization of rDNA genes in the woody medic species from the agronomically important Medicago section Dendrotelis was analysed to gain insight into their taxonomic relationships, to assess the levels of infraspecific variation concerning ribosomal loci in a restricted and fragmented insular species (M. citrina) and to assess the nature of its polyploidy.
METHODS
Fluorescence in situ hybridization (FISH) was used for physical mapping of 5S and 45S ribosomal DNA genes in the three species of section Dendrotelis (M. arborea, M. citrina, M. strasseri) and the related M. marina from section Medicago. Genomic in situ hybridization (GISH) was used to assess the genomic relationships of the polyploid M. citrina with the putatively related species from section Dendrotelis.
KEY RESULTS
The diploid (2n = 16) M. marina has a single 45S and two 5S rDNA loci, a pattern usually detected in previous studies of Medicago diploid species. However, polyploid species from section Dendrotelis depart from expectations. The tetraploid species (2n = 32) M. arborea and M. strasseri have one 45S rDNA locus and two 5S rDNA loci, whereas in the hexaploid (2n = 48) M. citrina four 45S rDNA and five 5S rDNA loci have been detected. No single chromosome of M. citrina was uniformly labelled after using genomic probes from M. arborea and M. strasseri. Instead, cross-hybridization signals in M. citrina were restricted to terminal chromosome arms and NOR regions.
CONCLUSIONS
FISH results support the close taxonomic interrelationship between M. arborea and M. strasseri. In these tetraploid species, NOR loci have experienced a diploidization event through physical loss of sequences, a cytogenetic feature so far not reported in other species of the genus. The high number of rDNA loci and GISH results support the specific status for the hexaploid M. citrina, and it is suggested that this species is not an autopolyploid derivative of M. arborea or M. strasseri. Further, molecular cytogenetic data do not suggest the hypothesis that M. arborea and M. strasseri were involved in the origin of M. citrina. FISH mapping can be used as an efficient tool to determine the genomic contribution of M. citrina in somatic hybrids with other medic species.
背景与目的
对豆科苜蓿属中具有重要农学意义的木本苜蓿亚属（Dendrotelis）的rDNA基因组织进行分析，以深入了解其分类关系，评估一个分布受限且碎片化的岛屿物种（柠条苜蓿）核糖体基因座的种内变异水平，并评估其多倍体的性质。
方法
采用荧光原位杂交（FISH）技术对木本苜蓿亚属的三个物种（乔木状苜蓿、柠条苜蓿、斯特拉瑟苜蓿）以及苜蓿亚属相关的滨海苜蓿的5S和45S核糖体DNA基因进行物理定位。利用基因组原位杂交（GISH）技术评估多倍体柠条苜蓿与木本苜蓿亚属假定相关物种的基因组关系。
主要结果
二倍体（2n = 16）滨海苜蓿有一个45S和两个5S rDNA基因座，这是苜蓿二倍体物种先前研究中通常检测到的模式。然而，木本苜蓿亚属的多倍体物种却与预期不同。四倍体物种（2n = 32）乔木状苜蓿和斯特拉瑟苜蓿有一个45S rDNA基因座和两个5S rDNA基因座，而在六倍体（2n = 48）柠条苜蓿中检测到四个45S rDNA和五个5S rDNA基因座。使用乔木状苜蓿和斯特拉瑟苜蓿的基因组探针后发现，柠条苜蓿没有一条染色体被均匀标记。相反，柠条苜蓿中的杂交信号仅限于染色体末端臂和核仁组织区（NOR）。
结论
FISH结果支持乔木状苜蓿和斯特拉瑟苜蓿之间密切的分类学亲缘关系。在这些四倍体物种中，NOR基因座通过序列物理丢失经历了二倍体化事件，这是该属其他物种迄今未报道的细胞遗传学特征。大量的rDNA基因座和GISH结果支持六倍体柠条苜蓿的特定地位，并且表明该物种不是乔木状苜蓿或斯特拉瑟苜蓿自多倍体衍生物。此外，分子细胞遗传学数据并不支持乔木状苜蓿和斯特拉瑟苜蓿参与柠条苜蓿起源的假说。FISH定位可作为一种有效的工具来确定柠条苜蓿在与其他苜蓿物种体细胞杂种中的基因组贡献。
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