长苞铁杉nrDNA ITS区假基因化拷贝的克隆及序列分析研究

Molecular Clone and Sequencing Analysis on Pseudogenized Copy of nrDNA ITS Region in Nothotsuga longibracteata

NrDNA作为一个重要的工具,在许多分类等级上被广泛地应用于系统发育的分析。以长苞铁杉(Nothotsuga longibracteata)为实验材料,通过nrDNA ITS区特异拷贝的克隆及假基因化分析,在序列水平上探讨假基因化的特征,进而探讨引起多拷贝基因家族假基因化的分子机制。实验结果表明:假基因化拷贝的序列长度为1 745 bp,比其它拷贝短11 bp-12 bp;GC含量明显偏低,特别是5.8 S区和ITS2区的GC含量分别比其它克隆低6.15%-6.17%和5.75%-6.15%;5.8 S区和ITS2区序列变异大,遗传距离(d)分别为0.0718+0.0221和0.0691+0.0178;在系统发育的分析中出现异常的长枝现象。

Nuclear ribosomal DNA （nrDNA） has been considered as an important tool for inferring phylogenetic relationships at many taxonomic levels. Based on molecular clone and sequencing analysis on one unique copy of nrDNA ITS region in Nothotsuga longibracteata, the structural characteristics of pseudogene were studied. Moreover, we discussed the molecular mechanism of pseudogenization. The results showed that the length of pseudogenic copy was 1 745 bp, and was 11 bp - 12 bp shorter than that of others. The GC content of pseudogenic copy was significantly lower. Especially, GC content were 6.15 % -6.17 % in 5.8 S region and 5.75 % -6.15 % in the ITS2 region lower than that of others. The marked sequence distance between pseudogenic copy and others were 0. 0718 ＋ 0. 0221 in 5. 8 S and 0. 0691 ＋ 0.0178 in ITS2 respectively. Phylogenetic analyses indicated that a unique position was in the phylogenetic trees with long terminal branch length.