樟属植物ITS序列多态性分析

Polymorphism of the Internal Transcribed Spacer of nrDNA in Cinnamomum Schaeffer(Lauraceae)

对樟科樟属(Cinnamomum Schaeffer)17个代表样本的核糖体DNA内转录间隔区(nr DNA ITS)进行克隆测序。对获得的87条不同ITS序列的长度变异、GC含量、5.8S区二级结构的稳定性、遗传距离、进化模式以及系统发育关系进行了相关分析。研究结果显示,ITS序列在樟属植物内存在明显的多态性,87条序列中的22条序列被鉴定为假基因序列,其余65条序列为功能基因序列;假基因序列采用中性进化模式,变异明显大于功能序列。ITS序列在樟属植物中出现一致性进化不完全和假基因现象也可能发生在樟科其它类群中,这可能是导致樟科植物ITS序列直接测序方式成功率低的重要原因。

In this study, nuclear ribosomal DNA （nrDNA） ITS fragments of 17 Cinnamomum samples were cloned and sequenced. A total of 87 different ITS sequences were obtained. Their length polymorphism, GC content, secondary structure stability of the 5.8S region, p-distance, evolutionary pattern and phylogenetic relationships were analyzed. The ITS sequences had a high degree of polymorphism. Among the 87 ITS sequences, 22 were pseudogenes and the other 65 were functional genes. The pseudogenes showed a neutral evolutional pattern and had a higher degree of polymorphism than functional genes. The incomplete concerted evolution of the ITS region and pseudogenes within the genus Cinnamomum may have also occurred in other Lauraceae plants, which could be responsible for the low sequencing success rate of the ITS region in Lauraceae plants.