【目的】检测大花序桉群体与环境适应性相关的基因组位点,为种质资源保护和利用提供分子生物学信息。【方法】利用84个SSR标记(包括29个基因组SSR 和55个EST-SSR)分析引种到广西,来源于澳大利亚昆土兰州北部和南部各7个大花序桉群体,通过Mantel 检验确定群体间是否存在地理隔离;检测群体间分化系数(Fst)离群值的受选择位点;并基于空间分析法检测与群体气候因子显著相关的等位片段,将显著相关位点的序列与NCBI数据库比对进行功能注释。【结果】大花序桉北部与南部群体间存在地理隔离,基于19个气候因子的聚类分析将北方与南方群体分为独立的组,这表明气候因子亦驱动了群体的分化。共检测到Fst离群值的受选择SSR位点39个(46.4%),其中,LOSITAN软件检测到12个正向选择位点和17个平衡选择位点。5个Fst离群值位点的6个等位片段与1个或多个气候因子显著相关(P<0.001),其等位频率在北部与南部群体间差异明显,其中,Embra6-118 bp与最冷月最低气温(Tmcm)显著相关,位点DNA序列的功能注释为碱性螺旋-环-螺旋(basic helix-loop-helix, bHLH)转录因子bHLH155;Embra20-121 bp与最暖季度降水量(Pwq)显著相关,位点的功能注释为蔗糖转运蛋白(sucrose transporters);EUCeSSR676-168 bp与Tmcm、Pwq、年均气温(Tma)和最暖月最高气温(Tmwm)均显著相关,位点的功能注释为光系统Ⅱ稳定性/组装因子HCF136 (photosystem II stability/assembly factor HCF136);另外两个显著相关位点EUCeSSR298和EUCeSSR1009的功能未知。【结论】大花序桉北部与南部群体的显著分化受长期气候的影响,在第四纪大冰期可能存在北部和南部避难所。与气候因子显著相关的SSR位点在北部和南部群体间的等位频率差异为基于正向选择的气候适应性提供了分子证据。
【Objective】 Genomic loci that are significantly associated with population adaptation were detected inEucalyptus cloeziana F. Muell. populations to obtain useful molecular information for germplasm conservation and utilization. 【Method】 Seven northern and southern populations of E. cloeziana were analyzed using 84 simple sequence repeats (SSR) markers [29 genomic SSRs and 55 expressed sequence tag (EST) derived SSRs]. Isolation by distance (IBD) among populations was determined using Mantel test. Outlier loci ofF-statistics of between-population differentiation (Fst) and their significant allelic associations with habitat climatic variables were investigated for all the SSR loci, with further functional annotation of the significantly associated loci against the NCBI non-redundant protein database. 【Result】 IBD was revealed between the northern and southern populations of E.cloeziana, and the clustering analysis based on 19 climatic variables also resulted in division of the northern and southern populations into independent groups, suggesting the climatic effect on driving the population divergence. A total of 39 Fst outliers (46.4%) were identified as selective loci. Specifically, the software LOSITAN detected 12 positive and 17 balancing selection loci. Six alleles from five outlier loci were identified with spatial analysis methods, each associated significantly with one or more climatic factors (P < 0.001) and showed dramatic difference in allelic frequency between the northern and southern populations. Among the six significant alleles, Embra6-118 bp was associated with the minimum temperature of the coldest month ( Tmcm), with the locus Embra6 functionally annotated as basic helix-loop-helix (bHLH) transcript factor bHLH155. The allele Embra20-121 bp was associated with the precipitation of the warmest quarter (Pwq), with Embra20 functionally annotated as sucrose transporters. EUCeSSR676-168 bp was associated with Tmcm, Pwq, the mean annual temperature (Tma) and the minimum temperature of the warmest month (Tmwm), with the locus functionally annotated as photosystem II stability/assembly factor HCF136. However, the two other significant markers EUCeSSR298 and EUCeSSR1009 were of unknown function. 【Conclusion】 The divergence between the northern and southern populations of E. cloeziana was strongly related with historical climate, and there might be glacial refugia in the northern and southern zones during the Quaternary. The marked difference in the frequency of climate-associated SSR alleles between the northern and southern populations provides molecular evidence for positive selection oriented climatic adaptation in E. cloeziana.
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