Quandt D, Stech M
Nees-Institut für Biodiversität der Pflanzen, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 170, 53115 Bonn, Germany.
Plant Biol (Stuttg). 2004 Sep;6(5):545-54. doi: 10.1055/s-2004-821144.
Structure, variability, and molecular evolution of the trnT-F region in the Bryophyta (mosses and liverworts) is analyzed based on about 200 sequences of the trnT-L spacer and trnL 5' exon, 1000 sequences of the trnL intron, and 800 sequences of the trnL 3' exon and trnL-F spacer, including comparisons of lengths, GC contents, sequence similarities, and functional elements. Mutations occurring in the trnL 5' and 3' exons, including compensatory base pair changes, and a transition in the trnL anticodon in Takakia lepidozioides, are discussed. All three non-coding regions display a mosaic structure of highly variable elements (V1 - V3 in the trnT-L spacer, V4/V5 corresponding to stem-loop regions P6/P8 in the trnL intron, and V6/V7 in the trnL-F spacer) and more conserved elements. In the trnL intron this structure is a consequence of the defined secondary structure necessary for correct splicing, whereas in both spacers conserved regions are restricted to promoter elements. At least the highly variable regions in the trnT-L spacer and stem-loop region P8 of the trnL intron seem to evolve independently in the major bryophyte lineages and are therefore not suitable for high taxonomic level phylogenetic reconstructions. In mosses, a trend of length reduction towards the more derived lineages is observed in all three non-coding regions. GC contents are mostly linked to sequence variability, with the conserved regions being more GC rich and the more variable AT rich. The lowest GC values (< 10 %) are found in the trnT-L spacer of mosses. In addition to two putative sigma (70)-type promoters in the trnT-L spacer, a third putative promoter is present in the trnL-F spacer, although trnL and trnF are assumed to be co-transcribed. Consensus sequences are provided for the -35 and -10 sequences of the major bryophyte lineages. The third promoter is part of a hairpin secondary structure, whose loop region is highly homoplastic in mosses due to an inversion occurring independently in non-related taxa, even at the intraspecific level.
基于约200个trnT-L间隔区和trnL 5'外显子序列、1000个trnL内含子序列以及800个trnL 3'外显子和trnL-F间隔区序列，对苔藓植物（苔藓和地钱）中trnT-F区域的结构、变异性和分子进化进行了分析，包括长度、GC含量、序列相似性和功能元件的比较。讨论了trnL 5'和3'外显子中发生的突变，包括补偿性碱基对变化，以及塔氏苔藓（Takakia lepidozioides）中trnL反密码子的转换。所有三个非编码区都呈现出高度可变元件（trnT-L间隔区中的V1 - V3、trnL内含子中对应于茎环区域P6/P8的V4/V5以及trnL-F间隔区中的V6/V7）和更保守元件的镶嵌结构。在trnL内含子中，这种结构是正确剪接所需的特定二级结构的结果，而在两个间隔区中，保守区域仅限于启动子元件。至少trnT-L间隔区中的高度可变区域和trnL内含子的茎环区域P8似乎在主要苔藓植物谱系中独立进化，因此不适合用于高分类水平的系统发育重建。在苔藓中，在所有三个非编码区都观察到朝着更进化谱系长度缩短的趋势。GC含量大多与序列变异性相关，保守区域富含GC，可变区域富含AT。在苔藓的trnT-L间隔区中发现了最低的GC值（< 10%）。除了trnT-L间隔区中的两个假定的sigma（70）型启动子外，trnL-F间隔区中还存在第三个假定的启动子，尽管trnL和trnF被认为是共转录的。给出了主要苔藓植物谱系的-35和-10序列的共有序列。第三个启动子是发夹二级结构的一部分，由于在非相关类群中甚至在种内水平独立发生的倒位，其环区在苔藓中高度同源。
