| The Sect.Chrysantha Chang,named for its golden petals,belongs to Camellia of Theaceae and has high ornamental,medicinal and economic values.At present,all the Sect.Chrysantha Chang plants have been listed as the first class protected species and the second class protected plants in the newly released List of National Key Protected Wild Plants.Due to similar morphology,difficult collection,natural hybridization and variation etc.,their taxonomic and interspecific relationships have been controversial.Meanwhile,the characteristics and related evolution of chloroplast are still unclear.Here,we reported23 Camellia chloroplast(cp)genomes from China by Illumina Hiseq Platform.We compared these cp genomes by bioinformatics methods to explore the interspecific relationships and evolution pattern of cp genome.The research contents and conclusions are as follows:All the cp genomes of the 23 Sect.Chrysantha Chang,Similar with most angiosperms,exhibit a typical quadripartite structure(LSC-IR-SSC-IR).The cp genome sizes,structures and gene compositions of most species in this Sect.were similar,and no structural inversion or gene rearrangement occurred.Such as,the cp genome sizes of most species are concentrated in ～157 kb and encoding a total of 118 genes,which distributed in 81 protein-coding genes(PCGs),32 t RNAs,and four r RNA genes,and one pseudogene(ycf1).The average GC content was 37.3%(only C.ptilosperma that was 37.4%).Due to lack three PCGs(psb C,psb D and psb Z)in the LSC region,the genome size of C.chrysanthoides is ～152 kb.Similar to most angiosperms,the IR regions are expanded/contracted in the Sect.Chrysantha Chang plastomes and this resulted in pseudogenization of boundary gene(ycf1).In this study,we identified 1036 interspersed repeats,484 tandem repeats and 1620 simple sequence repeats(SSRs)in the Sect.Chrysantha Chang cp genome.The majority of SSRs were mononucleotide repeats(A/T,72%).Moreover,most SSRs were distributed in the non-coding regions of the genome,namely the intergenic and intron regions.In addition,For the other four species,namely C.huana,C.pubipetala,C.pingguoensis var.terminalis and C.parvipetala,their two IR regions length were inconsistent due to the numbers of an 18 bp repeat sequence(‘attgatgctagtgacgat’)in their ycf2 gene.Finally,six hyper-variable regions with Pi values > 0.003 were detected,including three intergenic spacers(trn K(UUU)-rps16,trn L(CAA)-ndh B and rpl32-trn L(UAG))and three gene regions(rpo A,rps8 and ycf1).These polymorphic loci might be helpful for phylogenetic inference and population genetic studies of the genus Camellia.Phylogenetic results generated the same topology,which 23 Sect.Chrysantha Chang species formed two strongly supported(BS = 100/99,and PP = 1.0)clades.C.tunghinensis and C.euphlebia are sister species to each other,and they are closely related to C.nitidissima.Our results are also supported to regard the C.nitidissima var.macrocarpa,C.pingguoensis var.terminalis and C.wumingensis as separate species,and merge C.multipetala and C.longgangensis var.patens into one species.In addition,through analyzing the geographical distribution of sampling sites of each species,it was found that the phylogenetic relationship of Sect.Chrysantha Chang was closely related to its geographical distribution.The close or identical geographical distribution would result in similar environmental conditions such as water and soil physical and chemical properties,which would affect the phylogenetic relationship of Sect.Chrysantha Chang.In conclusion,this study reported the whole chloroplast genomes of 23 Sect.Chrysantha Chang species,which greatly enriches the genetic resources of Camelia species.Meanwhile,studying the evolutionary model and phylogenetic relationship also provides a solid theoretical reference for biodiversity conservation,rational exploitation and taxonomic revision of species. |
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