| The genus Bidens L.belongs to the tribe Coreopsidinae of Asteraceae and is mainly distributed in tropical and subtropical regions.The center of species diversity is located in the Americas.About 10 Bidens species are distributed in China.Species in the genus distributed in China are divided into two sections: Sect.Psilocarpae and Sect.Platycarpae.However,there are few reports on the phylogeny of Bidens in China.The relationship among species in Bidens and relationships with related genera are still controversial.Morphological characteristics of Bidens in China and their taxonomic value,comparison of chloroplast genome characteristics and phylogenetic relationship among species and related genera were mainly discussed in this research.Field population survey,specimen research and morphological characteristics analysis,comparative analysis of chloroplast genomes,and molecular phylogeny analysis based on the chloroplast genome and nuclear fragments were used to carry out the study.A basis for the taxonomic and systematic study of Bidens in the world will be provided by this study.The results of the study are as follows:1.Through field surveys and a large number of specimen studies,it is confirmed that a total of 11 species and 1 variety of Bidens are distributed in China.Through the observation,research and statistical analysis of the morphological characteristics of Bidens in China,a total of 17 morphological traits were screened out.The results of principal component analysis and cluster analysis based on 17 morphological traits showed that the Chinese Bidens species were divided into two branches.Clade I is a group with slender achenes,achene length and width ratio more than 10,and a round achene scar shape.Clade II is a group with flat achenes,length and width ratio less than5,and a long oval shape of achene scar.Shape of achene and shape of achene scar are important classifications between the two sections of Bidens.Characteristics such as achene spine direction,involucre shape,ray flower,number of disk crown lobes,calycular bracts shape and leaf segments have certain differences among Bidens,which carry important taxonomic value in interspecific identification.2.Based on next-generation sequencing technology,15 taxa of Bidens from China(belonging to 10 species and 1 variety)and 4 taxa in related genera from Coreopsis L.,Cosmos Cav.and Dahlia Cav.were sequenced.19 complete chloroplast genomes,19 ETS sequences and 19 ITS sequences were finally obtained.Comparative analysis of the chloroplast genome showed that the size of the chloroplast genome of Bidens was among 150237bp?151749bp,with a total of 134 annotated genes,including 87 proteincoding genes,37 t RNA genes,8 r RNA genes,and 2 pseudogenes.GC content was stable around 37.5%.Ten gene regions with large variation and ten intergenic regions with large variation were screened out by chloroplast genome sequence divergence analysis.These regions with most significant divergence can be used as potential molecular markers for molecular systematic studies of Bidens and related genera.No significant difference of the boundary of IRs was found among Bidens.The codon preference of the chloroplast genome is consistent within the genus.The third base of the codon prefers A / U.A total of 47 RNA editing sites were screened,all of which were the conversion of bases from C to U.The number and type of repetitive sequences are consistent within the genus,and repeats are mostly distributed in the intergenic regions of LSC and SSC.Analysis of gene selection pressure showed that clp P is undergoing positive selection in Bidens,which is speculated to be related to the changes in the taxa between Sect.Platycarpae and Sect.Psilocarpae of Bidens in China and the adaptability of invasive species to variable environments.3.The phylogenetic relationship reconstruction results based on the chloroplast genome and nuclear gene fragments showed that Bidens in China is a paraphyletic group.The genus was divided into two sections,namely Clade I(Sect.Platycarpae)and Clade II(Sect.Psilocarpae).Taxa in Sect.Platycarpae were crossed with taxa in Coreopsis.Species in Sect.Platycarpae are widely distributed in temperate regions,usually with broad achenes,including B.cernua,B.frondosa,B.tripartita,B.radiata,B.maximovicziana,and B.leptophylla.B.leptophylla is endemic to China,closely related to B.maximovicziana and B.tripartita in the phylogenetic relationship.Sect.Psilocarpae was clustered with Sect.Campylotheca and Sect.Steppia,which are also distributed in tropical and subtropical regions.Species in Sect.Psilocarpae are usually armed with long and slender achenes,including B.alba,B.alba var.radiata,B.pilosa,B.bipinnata,B.biternata and B.parviflora.Branching relationship was closely related to the geographical distribution and the achene morphology.It is recommended to separate the Sect.Platycarpae from Bidens. |
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