| Alien invasive plants have brought a series of ecological and economic problems,which has caused potential huge threats to human life.Studying the population expansion,evolutionary history and genetic structure changes during the expansion of alien plants is of great significance for revealing their invasion mechanism and prevention and control management.Verbena officinalis Linn.has a long history of application in China as a naturalized alien species,but its expansion and evolutionary history are still unclear.In the present study,we analyzed the expansion history and genetic structure of V.officinalis using intergenic region of cp DNA（trnL-trnF、psbD-trnT）and ITS sequences as well as reduced-representation genome sequencing.The main results are as follows:（1）Verbena bonariensis and V.brasiliensis are taken as out group.The intergenic region of cp DNA（trn L-trn F、psb D-trn T）and ITS sequences of 56 V.officinalis local populations（including the American population MN）were sequenced.The results indicates that V.officinalis in China produced a total of 10 haplotypes,with haplotype diversity Hd=0.482,nucleotide diversityπ=0.00024,which indicated that V.officinalis had low genetic diversity.The haplotype Hap-8 of V.officinalis is an ancestral haplotype,which evolved into haplotypes Hap-9 and Hap-10.And the widely distributed haplotype Hap-5 is also derived from Hap-8,while the other haplotypes are all derived from Hap-5 through one or two steps of mutation differentiation.（2）Because the similarity between local populations of V.officinalis was too high,the 55 populations of Verbascum were divided into 11 groups to analyze their genetic structure with reference to simplified genomic grouping.The results showed that the genetic diversity Ht=0.540,the average genetic diversity Hs=0.469,and the genetic differentiation coefficient Nst（0.156）between populations was greater than Gst（0.131）,but not significant（P>0.05）,indicating that V.officinalis don’t have obvious lineage differentiation structure.AMOVA analysis showed that genetic variation in V.officinalis mainly occurs within populations,with moderate differentiation between populations;The analysis of population historical dynamics shows that the V.officinalis population has experienced rapid expansion in history,as well as in the Northwest and Middle East regions.（3）Specific-Locus Amplified Fragment Sequencing（SLAF-seq）were performed on 181 V.officinalis materials from 51 populations（including the American population MN）after excluding 5 populations that were too close geographically.953Mb Reads data were obtained,with an average Q30 of 93.65%and an average GC content of37.96%,which indicated that the sequencing quality was good.A total of 1,452,374SLAF markers were developed,including 105,840 polymorphic SLAF markers.383,262 population SNP markers developed subsequently,and 93513 high-consistency SNP loci were obtained after filtration for subsequent analysis.（4）The 50 populations in China were regroup into 11 groups based on the analysis results of the above data and geographical distribution.And then evaluate their genetic diversity using SNP locus.The results showed that the mean expected heterozygosity（He=0.217）,the mean observed heterozygosity（Ho=0.089）,the mean Nei diversity index（h=0.245）and the mean Shannon index（I=0.318）of the V.officinalis population were all at low levels.Among them,the XN1 population in Southwest China was the highest in genetic diversity,and the HD2 population in East China was the lowest.（5）The results of phylogenetic trees,Admixtures,and PCA analysis revealed that11 groups of V.officinalis in China can be divided into 3 lineages:Southwest,Middle East,and Northwest.Among them,the XN1 group in the Southwest region and the HN group in the South China region formed the Southwest Lineage,the Middle East Lineage was comprised of the HZ1,HZ2,and HZ3 groups in the East China region and the HD1,HD2,and HD3 groups in the Central China region,and the XN2,XN3 groups in the Southwest region and the XB group in the Northwest region formed the Northwest Lineage.In addition,the historical gene flow prediction results showed that there was no population hybrid event among V.officinalis groups.（6）Combining above results and historical records,we speculated that the possible expansion history of V.officinalis.It may have invaded Yunnan during the Han Dynasty or earlier,and later spread from its origin to Southern China and Jiangnan regions.At the same time,it also spread northward to Prachuab and Guanzhong regions;and then V.officinalis rapidly spread from Guanzhong to Central and Eastern China,gradually evolving into the existing genetic pattern of V.officinalis.The differentiation of the Middle East lineage was influenced by the combined effects of the Southwest and Northwest lineages.The whole diffusion process of V.officinalis was closely related to human activities,mountains and rivers. |
