植物学报 ›› 2010, Vol. 45 ›› Issue (03): 345-353.DOI: 10.3969/j.issn.1674-3466.2010.03.006

• 研究报告 • 上一篇    下一篇

玉米rRNA基因的组织和表达模式

佘朝文1,2*; 蒋向辉1,2; 宋运淳3   

  1. 1怀化学院生命科学系, 怀化 418008; 2怀化学院民族药用植物资源研究与利用湖南省重点实验室, 怀化 4180083武汉大学生命科学学院植物发育生物学教育部重点实验室, 武汉 430072
  • 收稿日期:2009-12-11 出版日期:2010-03-01 发布日期:2010-05-01
  • 通讯作者: 佘朝文

Analysis of Organization and Expression Pattern of rRNA Gene in Maize

Chaowen She1,2*; Xianghui Jiang1,2; Yunchun Song3   

  1. 1Huaihua University, Huaihua 418008, China;
    2Huaihua University, Huaihua 418008, China;
    3College of Life Sciences, Wuhan University, Wuhan 430072, China
  • Received:2009-12-11 Online:2010-03-01 Published:2010-05-01
  • Contact: Chaowen She

摘要: 玉米(Zea mays)只有1对45S rDNA位点并在分裂期染色体形成次缢痕, 是研究植物细胞rRNA基因组织和表达模式的简单模型。采用荧光原位杂交(fluorescence in situ hybridization, FISH)、CPD(PI与DAPI组合)染色和银染技术, 分析了玉米根尖分生细胞rRNA基因的组织和表达模式。45S rDNA探针在所有间期细胞核中显示2种杂交信号: 荧光强烈地位于核仁周边的纽, 而相对较弱地分布于核仁内的点。在部分细胞中可观察到点与纽相连或从纽发出; 点的数目越多, 纽变得越小; 点的数目多少与细胞的活性呈正相关。研究结果表明, 纽代表了处于凝缩状态的非活性的rDNA染色质, 纽解凝缩形成的点是rRNA基因活跃转录的细胞学表现; 不同阶段间期核的点的数目变化反映了被活化的rRNA基因数目不同。间期和前期细胞的CPD染色和相继的银染结果显示, 大部分rDNA染色质没有参与核仁的形成。rDNA FISH显示, 同一间期细胞的2个同源rDNA位点的表达水平存在差异, 同源染色体次缢痕的长度差异以及Ag-NOR和银染核仁的异态性进一步证实了这种差异的存在。FISH结果显示, 早中期细胞的rDNA染色质相对解凝缩, 银染在所有早中期细胞和部分中期细胞显示了明显的核仁, 表明玉米的rRNA基因在有丝分裂早中期有较活跃的转录, 其转录在晚中期才停止。

Abstract: Maize (Zea mays L.) has a single pair of 45S rDNA sites that forms secondary constrictions in mitotic cells, and thus presents a simple model for studying the organization and expression pattern of rRNA genes in plants. We analyzed the organization and expression pattern of rRNA genes in root-tip meristematic cells of maize by fluorescence in situ hybridization (FISH), combined PI and DAPI (CPD) staining and silver staining. An 45S rDNA probe revealed two types of signals in all interphase nuclei: strongly fluorescing perinucleolar knobs and less-strongly fluorescing intranucleolar spots. The spots associated with or emanating from knobs were observed in a portion of nuclei. The more spots shown, the smaller are the knobs, and the number of spots was correlated with the activity of interphase cells. Thus, knobs represent condensed inactive rDNA chromatin, and the formation of spots decondensed from knobs is the cytogenetic manifestation of active rRNA gene transcription. The variation in number of spots among nuclei of different stages reflects the difference in number of activated rRNA genes. Sequential CPD and silver staining in interphase and prophase cells revealed that most of the rDNA chromatin did not participate in the formation of the nucleolus. The interphase rDNA FISH results also showed that the level of expression differed between the homologous 45S rDNA sites, which was further confirmed by the difference in length of secondary constriction of homologous chromosomes and differences in the size of homologous Ag-NORs and nucleoli. FISH results showed that the rDNA chromatin in prometaphase cells was relatively decondensed, and silver staining showed the existence of prominent nucleoli in all prometaphase cells and a portion of metaphase cells. These findings indicate that rDNA transcription is active during prometaphase and does not stop until late metaphase.