中文摘要：

【目的】检测和分析稀有放线菌中新的线型质粒。【方法】从植物内生菌中分离链霉菌之外的放线菌菌株，检测、测序和分析线型质粒。【结果】从中草药植物紫花前胡的叶片中分离到一株内生放线菌25L-1-1c，经过16S rRNA基因序列比对属于拟诺卡氏菌。从该菌株中检测到一个约25 kb的线型质粒pNPL1。克隆和测序了pNPL1新的端粒，含有多个小的回文序列。测序获得全长为24 621 bp的线型质粒pNPL1，预测编码22个基因，其中2个基因与链霉菌质粒的端粒复制基因同源，1个基因与链霉菌质粒主要的接合转移基因相似，其余19个基因为未知功能。携带pNPL1端粒复制基因的质粒不能转化变铅青链霉菌，暗示需要发展拟诺卡氏菌的遗传操作系统。【结论】这是首次在拟诺卡氏菌中发现和描述线型质粒。

英文摘要：

[Objective] To detect and analyze linear plasmids from rare actinomycetes species. [Methods] Rare actinomycetes strains were isolated from plants, and linear plasmids were detected, sequenced and analyzed. [Results] An endophytic actinomycetes strain 25L-1-1c was isolated from Chinese herb Peucedanum decursivum. Its 16S rRNA gene sequence resembled Nocardiopsis. Strain 25L-1-1c harbored a linear plasmid pNPL1. The telomere of pNPL1 was cloned and sequenced, which was a novel sequence containing multiple palindromes. The complete nucleotide sequence of pNPL1 comprised 24 621 bp, encoding 22 genes, 2 of them resembling Streptomyces telomere replication genes, one major plasmid transfer gene, and others unknown functional genes. Plasmid containing the Nocardiopsis telomere replication genes could not propagate in S. lividans, indicating that development of Nocardiopsis genetic system is needed. [Conclusion] This is the first example of linear plasmid in Nocardiopsis.