Department of Plant Anatomy and Cytology, University of Silesia, Katowice, Poland.
Cell Mol Biol Lett. 2012 Dec;17(4):526-41. doi: 10.2478/s11658-012-0025-4. Epub 2012 Aug 15.
The genus Brachypodium has become the target of extensive cytomolecular studies since one of its representatives, B. distachyon, has been accepted as a model plant for temperate cereals and forage grasses. Recent preliminary studies suggested that intraspecific rDNA polymorphism can occur in at least two members of the genus, B. sylvaticum and B. pinnatum, so the aim of this study was to further analyse this phenomenon. FISH with 25S rDNA and 5S rDNA probes was performed on somatic metaphase chromosomes, supplemented by the silver staining technique which distinguishes transcriptionally active from inactive 18S-5.8S-25S rDNA loci. The number, size and chromosomal distribution of 5S rDNA loci were very constant: two loci were invariably observed in all studied diploid accessions of both species, while four 5S rDNA loci were present in the tetraploid B. pinnatum. In contrast to 5S rDNA loci, those of the 35S rDNA were more variable. Two or three loci were observed in the diploid B. pinnatum and four in tetraploid accessions. In chromosome complements of B. sylvaticum accessions from two to six 35S rDNA sites were detected. Regardless of total rDNA locus number, only two were transcriptionally active in diploid accessions of both species, while two or four were active in the tetraploid B. pinnatum. Additionally, the fluorescent CMA/DAPI banding method was used to identify the relation between rDNA sites and CMA+ bands. It was revealed that the number and chromosomal distribution of CMA+ bands are in congruence only with 35S rDNA loci which gave strong FISH signals.
短柄草属已成为广泛细胞分子研究的目标，因为其代表之一，短柄草，已被接受为温带谷类作物和饲料草的模式植物。最近的初步研究表明，种内 rDNA 多态性至少可能发生在属中的两个成员，B. sylvaticum 和 B. pinnatum 中，因此本研究的目的是进一步分析这种现象。用 25S rDNA 和 5S rDNA 探针进行体细胞中期染色体的 FISH 实验，并用银染技术进行补充，该技术可区分转录活跃和不活跃的 18S-5.8S-25S rDNA 基因座。5S rDNA 基因座的数量、大小和染色体分布非常恒定：在两种物种的所有研究的二倍体材料中，始终观察到两个基因座，而四倍体 B. pinnatum 则存在四个 5S rDNA 基因座。与 5S rDNA 基因座相比，35S rDNA 基因座的变化更大。在二倍体 B. pinnatum 中观察到两个或三个基因座，而在四倍体中观察到四个基因座。在 B. sylvaticum 材料的染色体组成中，检测到二倍体中的 2 到 6 个 35S rDNA 位点。无论总 rDNA 基因座数量如何，只有两个在两种物种的二倍体材料中是转录活跃的，而在四倍体 B. pinnatum 中则有两个或四个是转录活跃的。此外，还使用荧光 CMA/DAPI 带型法来鉴定 rDNA 位点与 CMA+带之间的关系。结果表明，CMA+带的数量和染色体分布仅与发出强 FISH 信号的 35S rDNA 基因座一致。
