Exploring The Effects Of Polyploidy On Population Differentiation And Fitness Of Chamerion Angustifolium Based On Reduced-representation Genome Sequencing

Polyploidy provides an important driver for species diversification and adaptation to the environment.Chamerion angustifolium,belonging to Chamerion genus of Onagraceae family,is widely distributed in northern temperate and boreal regions.At present,it has been found that C.angustifolium has autotetraploid,hexaploid and a few rare cell types.Taking C.angustifolium as the research object,preliminary studies were carried out on the interaction between different cell types,phenotypic differentiation and polyploidy mechanisms.However,the impact of polyploidy on the adaptation of C.angustifolium population:What causes the complex distribution pattern of polyploidy?What is the molecular mechanism of polyploid ecological adaptation?There are still problems of insufficient natural sample size and lack of interpretation of genomic and macro-ecological data.In this study,C.angustifolium was used as the research material,and 309 samples from33 populations of C.angustifolium were sequenced by using GBS reduced-representation genome sequencing method.Combined with population genomics and landscape genomics,we explored the effect of polyploidy on the differentiation and adaptation of C.angustifolium population.The results are as follows:（1）Total 33 C.angustifolium populations were detected by flow cytometry,and 10diploid populations,16 tetraploid populations and 7 hexaploid populations were identified.GBS sequencing was performed on 309 samples of C.angustifolium,and 29,078 high-quality variant loci were finally screened through data analysis and processing;（2）The overall genetic diversity level of C.angustifolium was relatively high(₀0))=0.0418,=0.1441,=0.0445).The results of genetic diversity comparison among different ploidy of C.angustifolium populations showed that the nucleotide diversity（π）hexaploid（0.0468）was the largest,followed by the tetraploid population（0.0452）,and the diploid population（0.0417）was the smallest.However,the nucleotide diversity of different ploidy was not significantly different（P=0.2164）.Population genetic structure analysis showed that when=2,it was the optimal grouping,and C.angustifolium populations could be roughly divided into northern and southern clusters.PCA analysis distinguished Xinjiang populations from southern clusters.AMOVA analysis of C.angustifolium populations between different groups was carried out.Among the 33 C.angustifolium populations,the genetic differentiation between different groups（0.0525）was small;the genetic differentiation between populations based on high and low altitude grouping（0.0035）and the genetic differentiation between C.angustifolium populations grouped by different ploidy（0.0036）were both weak;（3）The simulation results of the population niche of C.angustifolium showed that among the climatic factors affecting the potential distribution area of C.angustifolium,the annual average temperature（45.1%）,the highest temperature in the warmest month（29.1%）and the annual average precipitation（16.6%）account for the environmental variables with the greatest contribution.The suitable areas of C.angustifolium are mainly in the mountainous areas of northeast,north,southwest and northwest regions,and there are differences in the potential distribution areas of C.angustifolium with different ploidy;（4）The gradient forest results showed that in the ranking of the importance of the selected climate environment variables,the annual average temperature,the seasonal variation coefficient of precipitation,the average daily temperature difference,and the annual precipitation had a greater impact on the allele frequency of the C.angustifolium population.The cumulative importance of population genetic variation along the environmental gradient showed that,in the diploid population of C.angustifolium,when the seasonal variation coefficient of precipitation was between 100 and 110,and the minimum temperature in the coldest month was between-22°C and-20°C,the allelic composition changed drastically;in the tetraploid population,when the average temperature of the year was between 0°C and 1°C,the highest temperature in the warmest month was between 22°C and 24°C,the allelic composition changed drastically;in the hexaploid population,the average temperature of the year was between 2°C and 3°C,the annual precipitation was between 350mm and 400mm,the seasonal variation coefficient of precipitation was between95 and 100,the allelic composition changed drastically.In conclusion,the study showed that polyploidy increases the genetic diversity of C.angustifolium population and drove the adaptation of C.angustifolium to different environments.Different ploidy of C.angustifolium populations had formed unique adaptation strategies for environmental factors of temperature and precipitation——Polyploid C.angustifolium populations can adapt to warmer and wetter environments,further revealing the importance of polyploidy to biological evolution.