苏铁nrDNA ITS区的序列多态性:不完全致同进化的证据

Intra-genomic polymorphism in the internal transcribed spacer (ITS) regions of Cycas revoluta:evidence of incomplete concerted evolution

本研究对苏铁(Cycas revoluta)nrDNAITS进行克隆测序,并以cDNAITS为参照,比较分析获得的序列的碱基变异、GC含量、5.8S二级结构的稳定性和5.8S保守基序的有无以及系统发育关系。结果发现苏铁nrDNAITS存在较高的基因组内多样性,同时,这些分化的nrDNAITS拷贝中包含有假基因的存在,而且假基因与功能拷贝之间已经形成了较大的遗传分化,这暗示假基因起源有较长历史。苏铁核仁组织区不仅多达16个,而且分布在13条染色体上,这可能是其nrDNAITS致同进化不完全的主要原因。

In the present study, a high intra-genomic polymorphism was detected in the internal transcribed spacer （including ITS 1, 5.8S and ITS2） regions of Cycas revoluta, suggestive of incomplete concerted evolution. Detailed comparisons of the ITS sequences from C. revoluta and those from other species further suggested that some divergent ITS paralogs from C. revoluta were likely pseudogenes. Some of these putative pseudogenes may have rather long evolutionary histories, because they have diverged substantially in sequences. We proposed that the incomplete concerted evolution in C. revoluta may have resulted from the high number and dispersed distribution of the nucleolus organizer regions （NORs） in the genome.