中文摘要：

根据已发表植原体质粒序列设计引物,经2次PCR扩增,获得大小不同的2段DNA片段,测序后拼接得到4种完整的环状质粒,分别是桑树萎缩植原体濮阳株系质粒（pMDPy）、长春花绿变植原体海南株系质粒（pPeVHn）、泡桐丛枝植原体山东株系质粒（pPaWBG33D）及苦楝丛枝植原体福清株系质粒（pCWBFq-2）,其中pMDPy为首次测定,其质粒全长分别为3833,3943,3843和3913bp,4种质粒皆编码5种蛋白,ORF1和ORF5分别编码复制相关蛋白（RepA）和单链DNA结合蛋白（SSB）,ORF2—4编码未知功能蛋白。4种质粒序列的非编码区分析表明,ORF1和ORF2之间的非编码区存在启动子和核糖体结合位点。将4种植原体质粒全序列与GenBank中登录的植原体质粒进行序列相似性比对和系统进化分析,结果表明这4种质粒与其他16SrⅠ组的质粒聚为一个大的分支,与16SrDNA系统发育树基本一致。这可为进一步深入了解不同植原体质粒的结构与功能、寄主专化性和质粒基因变异及进化奠定基础,也可为基于多基因分类鉴定提供新的理论依据。

英文摘要：

On the basis of the known phytoplasmal plasmid sequences,two pairs of specific primers were designed and used for amplication by PCR. Two amplified DNA fragments with different sizes covering the whole plasmid were obtained through two round of PCR amplification. After being sequenced and spliced,four phytoplasmal full-length circular plasmid DNA sequences, including the plasmids of mulberry dwarf （ pMDPy ） in Puyang,Henan Province, periwinkle （Catharanthus roseus） virescence （ pPEVHn ） in Hainan Province,paulownia witches ’-broom （ pPaWBG33D ） in Yanzhou,Shandong Province and chinaberry witches ’-broom phytoplasma strains （ pCWBFq-2 ） in Fuqing,Fujian Province were achieved,with the sizes of 3 833,3 943,3 843 and 3 913 bp,respectively. They are predicted to encode five proteins,open reading frame ORF1 encoding replication associated protein （ RepA）,ORF5 encoding binding protein （SSB）and ORF2-4 encoding given unknown function proteins. pMDPy is the first plasmid determined from mulberry dwarf phytoplasma. Sequence analysis of non-coding regions （ NCR） of the four kinds of plasmids revealed that the NCR sequences between ORF1 and ORF2 existed promoters and ribosome binding sites. The four phytoplasmal plasmid sequences were compared with the phytoplasmal plasmid sequences found in GenBank through multiple alignments and phylogenetic analysis; the results showed that these four plasmids and other 16Sr Ⅰ group plasmid could be grouped into a large branch,which is consistent with the phylogenetic tree created from 16S rDNA comparisons. This research would not only provide further insight into the different phytoplasmal plasmid structure and function,host specificity and plasmid variation and evolution within different phytoplasma species or strains,but also offer new theoretical basis for a multiple genes and index-based system for phytoplasmal classification.