Dipartimento di Biologia, Università di Pisa, via L. Ghini, 56100, Pisa, Italy.
Protoplasma. 2013 Jun;250(3):683-9. doi: 10.1007/s00709-012-0441-3. Epub 2012 Sep 5.
In this paper, we provide further information on the genome organisation of Haplopappus gracilis, one of the six angiosperms showing the lowest chromosome number, i.e. 2n = 4, by determining the nucleotide sequence of the intergenic spacer region of the ribosomal RNA genes and its cytological localization on metaphase chromosomes. DNA sequence analysis reveals the occurring of a product of 4,382 bp in length, characterised by the presence of four blocks of different repeated sequences. Our analysis also evidenced putative promoter regions with three transcription initiation sites for polymerase I, as previously reported in Artemisia absinthium, belonging to the same Asteraceae family. A fluorescent in situ hybridization with the intergenic spacer probe indicates the presence of rDNA genes only in the satellited chromosomes of H. gracilis; besides, differences in the signal intensity between homologous chromosomes were frequently observed, thus suggesting for these chromosome sites the presence of a variable number of rDNA gene copies, even if a divergent chromatin organisation in corresponding regions cannot be ruled out.
本文提供了关于矮甘菊基因组结构的进一步信息。矮甘菊是六种染色体数目最少的被子植物之一，其染色体数目为 2n=4。本研究通过测定核糖体 RNA 基因间隔区的核苷酸序列及其在中期染色体上的细胞遗传学定位，对其进行了研究。DNA 序列分析揭示了一个长度为 4382 个碱基的产物，其特征是存在四个不同重复序列的块。我们的分析还表明，与先前报道的菊科蒿属植物一样，存在三个聚合酶 I 转录起始位点的启动子区域。用基因间隔区探针进行荧光原位杂交表明，rDNA 基因仅存在于矮甘菊的卫星染色体中；此外，在同源染色体之间经常观察到信号强度的差异，因此表明这些染色体位点存在可变数量的 rDNA 基因拷贝，即使不能排除相应区域染色质组织的差异。
