Study On Chloroplast Genome Phylogeny And Morphological Evolution Of The Styracacea

Styracaceae DC.& Spreng is one of 22 families of Ericales,a large genus(Styrax)and 11 small genera,with about 160 species.It is distributed in East Asia,North America and Southern Europe.Important ornamental,medicinal,economic and protective value.The number of species and genes of Styracaceae used in molecular phylogenetic studies is increasing,but systematic studies on inter-genus are still incomplete.Regarding the research on the phylogenetic relationship between the genera of the Styracaceae,the results have low support rate(BS<50%),incomplete sampling,and unclear relationship.In order to study whether the structural characteristics of the plastid genome of Styracaceae,the phylogenetic relationship between genera and the evolution of morphological characteristics are consistent with the chloroplast genome,we obtained the plastid genome data by extracting leaf DNA and sequencing assembly,combined with the published sequence.In this study we collected 28 complete plastomes of Styracaceae,including 12 sequences newly reported here and 16 publicly available complete plastome sequences.Using the research methods of phylogenetic genomics,the phylogenetic framework of the Styracaceae was reconstructed.The main research results are as follows:(1)The chloroplast genome of the Styracaceae has a typical terrestrial angiosperm tetrad structure,composed of four parts: two inverted repeat regions,a large single copy region and a small single copy region;28 plastids of the Styracaceae is relatively consistent in genome size,GC content and other genomic features and structure.It encodes the same number of 113 different genes,including 79 protein-coding genes,30 t RNA genes and 4 r RNA genes.Except for the gene inversion of Alniphyllum Matsum and Bruinsmia Boerl.& Koord in the large single copy region,the sequence of all genes is consistent in these genomes,and the entire genome has a high degree of collinearity.(2)Nucleotide diversity analysis results show that there are more mutation sites in non-coding regions than coding regions.Like most angiosperms,the degree of evolution of non-coding regions is greater than protein coding regions.The inverted repeat region is very conservative.The mutation sites in the coding region and the non-coding region are lower than the two single-copy regions,and no obvious mutation hot spots were found;In positive selection analysis,we identified 7 positively selected coding genes(rps4,rpl23,acc D,rpo C1,psa A,rpo A,and ndh H).Styracaceae is dominated by synonymous substitutions.(3)Phylogenetic reconstructions of 28 sequences of Styracaceae and 3 extra groups based on seven data sets(i.e.,LSC,SSC,IR,Coding,Non-coding,combination of LSC+SSC and concatenation of LSC+SSC+one IR)produced similar topologies,except for the inverted repeat region.We using maximum likelihood(ML)and Bayesian method(BI)constructs a phylogenetic tree,but the latter has a certain improvement in the resolution of system relations and the support rate of most nodes.Studies have shown that the systematic positions of Changiostyrax dolichocarpa in the 7 phylogenetic trees are quite different,and Sinojackia and Pterostyrax are not monophyletic in the inverted repeat zone,and the positions of the other species are all consistent.The 7 sets of data matrices are not obvious The signal conflicts.Phylogenetic analysis of Styracaceae showed that Styrax,as the first differentiated group of Styracaceae,is a sister group with all species.Alniphyllum and Bruinsmia are clustered into one branch with the longest differentiation branch and a sequence of 20 Kb inversion.Huodendron is located between the genus Styrax and Alniphyllum + Bruinsmia,which is a sister group to each other.Perkinsiodendron does not form a branch with Halesia diptera,but gathers with Rehderodendron macrocarpum to form a high support.Halesia diptera and Melliodendron xylocarpum form a sister relationship.As the last differentiate,Pterostyrax and Sinojackia as,results strongly support the monophyly,except for the inverted repeat region.(4)The morphological characteristics of Styracaceae were analyzed.The results showed that the fruits of this family are quite different in shape.Most of them are drupe.Only Alniphyllum and Huodendron biaristatum are capsules.Exocarp is smooth or has ribs or wings,and Calyx campanulate,obconical,or cup-shaped.The morphological characteristics evolutionary tree constructed based on the plastid genome shows that the Styracaceae evolved from superior to inferior,and the corolla lobes evolved from imbricate to valvate,with small differences in shape,and the inflorescence from more flowers to less flowers.In evolution,the stamens of Styracaceae are twice as large as the corolla lobes,and there are no identical numbers.In the analysis of morphological evolution,Styrax has both the original shape and the evolutionary traits,with the widest distribution,indicating to a certain extent that other genera are derived from it.