Fransz P, Armstrong S, Alonso-Blanco C, Fischer T C, Torres-Ruiz R A, Jones G
School of Biological Sciences, University of Birmingham, Edgbaston, UK.
Plant J. 1998 Mar;13(6):867-76. doi: 10.1046/j.1365-313x.1998.00086.x.
A detailed karyotype of Arabidopsis thaliana is presented using meiotic pachytene cells in combination with fluorescence in situ hybridization. The lengths of the five pachytene bivalents varied between 50 and 80 microns, which is 20-25 times longer than mitotic metaphase chromosomes. The analysis confirms that the two longest chromosomes (1 and 5) are metacentric and the two shortest chromosomes (2 and 4) are acrocentric and carry NORs subterminally in their short arms, while chromosome 3 is submetacentric and medium sized. Detailed mapping of the centromere position further revealed that the length variation between the pachytene bivalents comes from the short arms. Individual chromosomes were unambiguously identified by their combinations of relative lengths, arm-ratios, presence of NOR knobs and FISH signals with a 5S rDNA probe and chromosome specific DNA probes. Polymorphisms were found among six ecotypes with respect to the number and map positions of 5S rDNA loci. All ecotypes contain 5S rDNA in the short arms of chromosomes 4 and 5. Three different patterns were observed regarding the presence and position of a 5S rDNA locus on chromosome 3. Repetitive DNA clones enabled us to subdivide the pericentromeric heterochromatin into a central domain, characterized by pAL1 and 106B repeats, which accommodate the functional centromere and two flanking domains, characterized by the 17 A20 repeat sequences. The upper flanking domains of chromosomes 4 and 5, and in some ecotypes also chromosome 3, contain a 5S rDNA locus. The detection of unique cosmids and YAC sequences demonstrates that detailed physical mapping of Arabidopsis chromosomes by cytogenetic techniques is feasible. Together with the presented karyotype this makes Arabidopsis a model system for detailed cytogenetic mapping.
利用减数分裂粗线期细胞结合荧光原位杂交技术，展示了拟南芥的详细核型。五条粗线期二价体的长度在50至80微米之间变化，这比有丝分裂中期染色体长20 - 25倍。分析证实，两条最长的染色体（1号和5号）是中着丝粒染色体，两条最短的染色体（2号和4号）是近端着丝粒染色体，其短臂末端带有核仁组织区（NORs），而3号染色体是亚中着丝粒染色体且中等大小。着丝粒位置的详细图谱进一步表明，粗线期二价体之间的长度差异来自短臂。通过相对长度、臂比、NOR结的存在以及5S rDNA探针和染色体特异性DNA探针的荧光原位杂交信号的组合，明确鉴定出了各个染色体。在六个生态型中发现了5S rDNA位点的数量和图谱位置方面的多态性。所有生态型在4号和5号染色体的短臂中都含有5S rDNA。在3号染色体上5S rDNA位点的存在和位置观察到三种不同模式。重复DNA克隆使我们能够将着丝粒周围的异染色质细分为一个中央结构域，其特征是pAL1和106B重复序列，该结构域包含功能着丝粒，以及两个侧翼结构域，以17 A20重复序列为特征的侧翼结构域。4号和5号染色体的上部侧翼结构域，在某些生态型中3号染色体也有，含有一个5S rDNA位点。独特的黏粒和酵母人工染色体（YAC）序列的检测表明，通过细胞遗传学技术对拟南芥染色体进行详细物理图谱绘制是可行的。连同所展示的核型，这使得拟南芥成为详细细胞遗传图谱绘制的模型系统。
