Interspecific Relationships And Genetic Structure Of Trapa L.in The Yangtze River

Trapa species are annual aquatic plants,distributing in Asian,Europe and Africa,it has certain economic and ecological value.Mid-lower Yangtze Basin and Heilongjiang-Tumen Basin are biodiversity distribution centers of Trapa,and due to the lack of genetic evidence,the driving factors influencing the geographic structure remanin unclear.There is great variation in the morphology of the genus of Trapa,and the taxonomic system of Trapa is controversial.There is no accepted taxonomic system so far.In this study,second generation sequencing technology was used to obtain 9 chloroplast genomes of Trapa.The phylogenetic tree was constructed and the phylogenetic relationship between the Trapa species and the related species was analyzed and discussed.Meanwhile,638 individuals from 31 populations of Trapa were selected as the research objects,and their genetic diversity,genetic structure were studied based on microsatellite markers.The main results and conclusions are as follows:(1)In this study,9 Trapa chloroplast genomes were obtained,and have the typical four division structure of angiosperm chloroplast genome.The whole chloroplast genome of T.quadrispinosa and T.bicornis var.taiwanensis were 155,554 bp and 155,543 bp,and both encode 79 protein genes,4 rRNA genes and 30 tRNA genes.The chloroplast genomes of Trapa were conserved,there were only a few structural differences in the boundary region,and the nucleotide variation main occurred in noncoding region.The phylogenetic tree constructed based on the chloroplast genomic data has high support rate,and the genus of Trapa was divided into 5 groups.Besides,we constructed phylogenetic tree based on conserved sequence and protein coding regions of chloroplast genome of 48 species of Myrtales respectively.The results show that the phylogenetic tree topology based on different data is generally consistent,the genus Sonneratia is closely related to the genus Trapa,and the genus Trapa can be thought of a monophyletic clade.(2)The genetic structure and genetic diversity of Trapa based on 20 pairs of microsatellite primers were studied.The results showed that the overall genetic diversity of the genus was low,the average observed heterozygosity(Ho)was 1.313,and the average expected heterozygosity(He)was 0.126.The gene flow between populations of Trapa was weak and different levels of genetic differentiation appeared among populations.Mantel analysis shows that there was a significant correlation between genetic distance and geographical distance in Trapa,geographic isolation further restricts gene flow,resulting in significant genetic differentiation between different populations of the same species.The results of STRUCTURE show that the population of Trapa could be clearly distinguished from other populations,PCoA analysis shows the same results.(3)The chloroplast genome and microsatellite analysis of Trapa showed that there were some differences between T.maximowiczii and other species,which indicates that Trapa has an important taxonomic status among the genus of Trapa.The results showed both the large species and small species concepts have certain limitations.The results of this study will provide a data basis for the future study of molecular systematics and genetic structure of the species.And further study should expand the sampling range,add molecular markers with higher diversity,and combine morphological traits for comprehensive analysis.