我国特有植物青檀遗传结构的ISSR分析

The genetic structure of endemic plant Pteroceltis tatarinowii by ISSR markers

青檀是我国特有的第三纪残遗植物,是宣纸纤维来源的重要原材料,现已被列入国家Ⅲ级保护植物。采用简单序列重复区间扩增多态性(ISSR)标记技术,对采自27个地理种群的628个青檀个体的遗传多样性和遗传结构进行了检测。8对引物共得到66个清晰的扩增位点,其中多态性位点63个,多态性位点百分率为95.45%。分析结果表明,青檀在物种水平上具有很高的遗传多样性(PPB=95.45%、Ao=1.9545、Ae=1.5729、He=0.3335、I=0.4980、Hb=0.3437)。在种群水平上的遗传多样性(PPB=69.98%、Ao=1.6998、Ae=1.4449、He=0.2561、I=0.3793、Hb=0.2656)和种群间遗传分化水平(Gst=0.23,ФST=0.25)均处于中等水平。华北地区(30°—42°N)和华南地区(22°—30°N)青檀的遗传多样性和遗传结构的差异并不显著。古老的起源历史、较广的分布范围、异交的繁育系统、风媒种子、长命的生活史以及华南和华北地形和植被的差异可能是导致青檀目前遗传格局的主要原因。结合叶绿体序列(cpDNA)序列的遗传结构特征对青檀的保护策略进行了探讨。

Pteroceltis tatarinowii Maxim.（Ulmaceae）,a tertiary relict plant of a temperate deciduous tree species endemic to China,is widely distributed in bare limestone mountains across the mainland in China.The bark（phloem fiber） of this plant has long since been used as the sole raw material for manufacturing Chinese traditional Xuan Paper.However,the species are subject to many threats due to its distribution pattern characterized by small patches;its decreasing population size resulted from overexploitation,and reduction of the original forest ecosystem.Thus,it has now been listed as a rare and endangered plant（National Grand III） in China. Using inter-simple sequence repeat markers,the genetic diversity and structure of 628 individuals from 27 populations of P.tatarinowii were detected.A total of 66 bands,of which 63 were polymorphic,were presented from the 8 selected primers screening across all samples,with the percentage of polymorphic bands up to 95.45%.The result of POPGENE revealed quite high level genetic diversity for the plant at the species level（PPB=95.45%,Ao=1.9545,Ae=1.5729,He=0.3335,I=0.4980）.At the population level,TS population from Gansu harbored the highest genetic diversity（PPB=84.85%,Ao=1.8485,Ae=1.5217,He=0.3033,I=0.4516）,whereas NL population from Guangdong with the lowest genetic variation（PPB=54.55%,Ao=1.5455,Ae=1.3135,He=0.1841,I=0.2756）.The mean population genetic level（PPB=69.98%,Ao=1.6998,Ae=1.4449,He=0.2561,I=0.3793） and population genetic differentiation of P.tatarinowii（Gst=0.23,ФST=0.25） were both at the middle level compared to other species.Gene flow（Nm） was estimated to be 1.65.In addition,different genetic variation and patterns were found between North China and South China.Populations of North China presented higher genetic diversity（PPB=95.45%,He=0.3332,I=0.4964） and lower genetic differentiation（ФST=0.22） than those of South China（PPB=93.94%,He=0.3220,I=0.4814 and ФST=0.25）.It would seem the extant genetic pattern of P.tatarinowii was might mainly attributed to its long evolutionary history,wide-ranging distribution,outcross mating system,long life cycle and complex differences of terrain and vegetation between North China and South China. According to our aforementioned results and the evidence from our cpDNA data,in situ conservation was the preferred way to maintain the species′ high level genetic diversity.Especially,much more attention should be paid to populations with higher genetic diversity（TS,JX and QY） and populations harboring peculiar cpDNA haplotypes（XA,SD,ML,NXS,LP,YF,WYS,GL,AL）.In the condition of establishment of artificial plantation and germplasm bank,the above peculiar populations should been given prior consideration.Regarding the genetic pattern difference between South China and North China,more populations in South China and fewer representative populations with more individuals in North China should been sampled to obtain the utmost genetic diversity of P.tatarinowii.