基于叶绿体和ITS序列的甘蒙柽柳谱系地理学研究

甘蒙柽柳(Tamarix austromongolica Nakai)是我国黄河流域特有种，具有较强的抗逆性，耐寒耐旱、耐盐碱，是维护岸堤稳定、改良土壤、防风固沙的优良树种。为了探寻甘蒙柽柳居群间的谱系进化关系，本研究利用四条叶绿体基因片段(psb A-trn H、trn T-trn L、trn L-trn F和trn Q-rp S16)和一条核基因片段ITS序列，通过PCR扩增、测序对甘蒙柽柳20个居群的叶片样品进行分析，研究了甘蒙柽柳的遗传多样性、谱系地理结构，以及黄河形成对甘蒙柽柳居群分布、遗传结构的影响。同时，通过对甘蒙柽柳的叶绿体全基因组测序分析，研究了甘蒙柽柳的系统进化及其种群的扩散历史。研究结果为甘蒙柽柳种质资源的保护利用提供理论依据。本研究主要结果如下:(1)甘蒙柽柳居群的遗传变异主要发生在居群内(cp DNA:66.2%;n DNA:73.9%)。叶绿体基因和核基因的遗传分化系数N_(ST)(cp DNA:0.24;n DNA:0.23)和G_(ST)(cp DNA:0.22;n DNA:0.25)差异均不显著(P>0.05)，表明甘蒙柽柳居群间无明显的谱系地理结构。这可能是由于甘蒙柽柳主要分布于黄河流域，其种子小且被毛，易于随风或水传播，促进了居群间的交流。(2)叶绿体单倍型H1、核基因单倍型R1频率最高，分布最广，且位于单倍型分布网络结构的中心位置，可能为古老单倍型，其余单倍型均由H1、R1分化而来。甘蒙柽柳居群单倍型网络结构呈星状分布，表明其居群间基因交流频繁，暗示该物种经历过快速扩张。中性检验结果Tajima’s D和Fu’s Fs均为负值，失配分析结果表明群体的期望扩张分布曲线与实际观测到的分布曲线基本吻合，均呈单峰分布，进一步证实该物种经历过快速扩张。(3)甘蒙柽柳代表性居群及其近缘物种的叶绿体测序结果表明，甘肃省永靖县附近的甘蒙柽柳位于系统发育树基部，暗示了该居群较为古老，该物种随着黄河的流向迅速向中下游迁移扩散。青海省同德县的甘蒙柽柳居群与其他居群的分化时间和黄河溯源加长切穿龙羊峡的时间基本一致，推测黄河的溯源侵蚀使得甘蒙柽柳居群从甘肃省永靖县附近迁移至上游。综上，本研究通过叶绿体全基因组、基因片段和核基因片段初步揭示了甘蒙柽柳居群间的谱系关系及黄河贯通形成对甘蒙柽柳现有分布格局的影响。研究结果有助于甘蒙柽柳的种质资源保存、优良性状固定以及新品种培育等工作的开展，为该物种的遗传改良及分子育种提供重要参考。

Tamarix austromongolica Nakai is an endemic species to the Yellow River basin in China, with strong stress resistance including cold, drought and salt tolerance. It is an excellent tree species for maintaining bank stability, improving soil, windbreak and sand fixation. To explore the phylogenetic and evolutionary relationships among its populations, this study analyzed leaf samples of 20 populations of T. austromongolica Nakai via PCR amplification and sequencing using four chloroplast gene fragments (psbA-trnH, trnT-trnL, trnL-trnF and trnQ-rps16) and one nuclear ribosomal internal transcribed spacer (ITS) sequence. The genetic diversity, phylogeographic structure, and the impact of the formation of the Yellow River on the distribution and genetic structure of T. austromongolica Nakai populations were investigated. Additionally, complete chloroplast genome sequencing was conducted to analyze the phylogenetic evolution and population dispersal history of this species. The results provide theoretical basis for the protection and utilization of T. austromongolica Nakai germplasm resources. The main findings are as follows:
(1) The genetic variation of T. austromongolica Nakai populations mainly occurs within populations (cpDNA: 66.2%; nDNA: 73.9%). The genetic differentiation coefficients N_ST (cpDNA: 0.24; nDNA: 0.23) and G_ST (cpDNA: 0.22; nDNA: 0.25) of chloroplast genes and nuclear genes show no significant differences (P > 0.05), indicating no obvious phylogeographic structure among populations. This may be due to the fact that T. austromongolica Nakai is mainly distributed in the Yellow River basin, and its small hairy seeds are easily dispersed by wind or water, promoting gene flow among populations.
(2) Chloroplast haplotype H1 and nuclear haplotype R1 have the highest frequency and widest distribution, and are located at the center of the haplotype network, likely representing ancestral haplotypes, while the remaining haplotypes are differentiated from H1 and R1. The haplotype network of T. austromongolica Nakai populations exhibits a star-like distribution, suggesting frequent gene flow among populations and indicating that this species has undergone rapid expansion. The results of neutrality tests (Tajima’s D and Fu’s Fs) are both negative, and mismatch distribution analysis shows that the expected expansion distribution curve is basically consistent with the actually observed distribution curve, both presenting a unimodal pattern, further confirming that this species has undergone rapid expansion.
(3) Chloroplast sequencing results of representative populations of T. austromongolica Nakai and its closely related species indicate that T. austromongolica Nakai near Yongjing County, Gansu Province is located at the base of the phylogenetic tree, suggesting that this population is relatively ancient, and this species rapidly migrated and dispersed to the middle and lower reaches along the flow of the Yellow River. The divergence time of T. austromongolica Nakai populations in Tongde County, Qinghai Province is basically consistent with the time when the headward elongation and incision of the Yellow River cut through the Longyang Gorge. It is speculated that the headward erosion of the Yellow River drove the migration of T. austromongolica Nakai populations from near Yongjing County, Gansu Province to the upper reaches.
In summary, this study preliminarily revealed the phylogenetic relationships among T. austromongolica Nakai populations and the impact of the formation and connection of the Yellow River on the current distribution pattern of this species based on complete chloroplast genome, chloroplast gene fragments and nuclear gene sequences. The results contribute to the conservation of germplasm resources, fixation of excellent traits and breeding of new varieties of T. austromongolica Nakai, providing important references for its genetic improvement and molecular breeding.

搜集汇总

背景与挑战

背景概述

该数据集基于叶绿体和ITS序列，研究了甘蒙柽柳的谱系地理学，分析了20个居群的遗传多样性和谱系结构。研究发现甘蒙柽柳的遗传变异主要发生在居群内，无显著地理结构，且物种经历过快速扩张，其分布与黄河形成密切相关，为种质资源保护提供了理论依据。