秦岭蕙兰种群遗传结构与基因流研究

Population genetic structure and gene flow of Cymbidium faberi in the Qinling Mountains

关键词:  蕙兰, 遗传多样性, 种群遗传结构, 基因流, 秦岭

Key words:  Cymbidium faberi, genetic diversity, population genetic structure, gene flow, Qinling Mountains

摘要:

蕙兰(Cymbidium faberi)属兰科兰属植物,野生蕙兰被列入联合国《濒危野生动植物种国际贸易公约》附录Ⅱ和中国珍稀濒危植物信息系统保护范围。秦岭是我国南北气候的地理分界线和重要的生态安全屏障。为了解秦岭野生蕙兰的遗传背景,该研究利用筛选出的2对叶绿体DNA psbA-trnH和rpl14-rpl36引物,对秦岭蕙兰15个种群271个个体进行序列扩增和测序,分析其遗传多样性,检测遗传结构并估算种群间基因流。结果表明:(1)秦岭蕙兰种群平均单倍型多样性为0.725,平均核苷酸多态性为3.1 × 10^-3,具有较高遗传多样性水平。(2)分子方差分析(AMOVA)结果表明,秦岭蕙兰遗传变异主要发生在种群内(88.84%),种群间遗传变异仅占11.16%,种群间遗传分化水平较低(Φ_ST=0.112,P<0.01),没有形成明显谱系地理结构。(3)基因流估算结果显示,除3个种群存在不对称双向基因流(迁出的基因流较强,迁入的基因流较弱)以外,其余种群间基因流强度(N_m)均大于1,表明秦岭蕙兰种群间种子介导的基因交流频繁。综上认为,蕙兰种子长距离传播和扩散能力可能是该遗传结构形成的原因,建议就地保护时优先保护单倍型多样性较高的LSZ和NCZ种群。该研究可为该物种种质资源保护提供理论依据。

Abstract:

Cymbidium faberi is a species of the genus Cymbidium in Orchidaceae. It is listed in Appendix Ⅱ of the Convention on International Trade in Endangered Species(CITES)and Information System of Chinese Rare and Endangered Plants(ISCREP). The Qinling Mountains are a geographically north-south climate boundary and an important ecological barrier in China. To understand the genetic background of wild C. faberi in this region, 271 samples from 15 populations were subjected to sequence amplification and sequencing, and were analyzed to evaluate the genetic diversity, genetic structure and gene flow among populations based on psbA-trnH and rpl14-rpl36 intergenic spacers of chloroplast DNA. The results were as follows:(1)The mean haplotype diversity was 0.725 and nucleotide diversity was 3.1 × 10^-3, indicating a high level of genetic diversity.(2)The results of analysis of molecular variance(AMOVA)revealed that as much as 88.84% of molecular variance was distributed within populations, only small percentage of the total genetic variation was attributed to genetic differences among populations(11.16%), and the level of genetic differentiation was low(Φ_ST = 0.112,P<0.01), and no obvious phylogeography structure was formed.(3)Estimation results of gene flow indicated that unidirectional gene flow moving from these populations to other populations was stronger than that from other populations. However, gene flow intensity(N_m)was superior to 1.0 in most cases, suggesting the presence of frequent seed-mediated gene flow between populations. In conclusion, long-distance dispersal and spread capabilities of C. faberi seeds may result in the lack of population genetic structure. It is recommend that LSZ and NCZ populations should be given priority for in-situ conservation because these two populations have much higher haplotype diversity. This study provides a theoretical basis for the conservation of germplasm resources of this species.