| Eragrostideae Stapf,the second-largest tribe in Chloridoideae(Poaceae),is a taxonomically complex tribe.There are about 500 species in this tribe,most of which are distributed in tropical and subtropical regions.According to the latest classification system of Soreng et al.,there are three genera in Chinese Eragrostideae,namely,Eragrostis,Harpachne,and Enneapogon.Among them,the species of Eragrostis are widely distributed,the interspecific relationship is ambiguous,and the interspecific characters exist cross phenomenon,so its systematic relationship has been controversial.Therefore,the systematic relationship between species has been controversial.Although the taxonomic research of Eragrostideae has made progress in morphology and molecular systematics,there are few species of Eragrostis studied in the past,and the applicability of the molecular markers used was limited.In this study,species from three genera of Eragrostis,Harpachne,and Enneapogon were selected for morphological study,species from four genera of Eragrostis,Harpachne,Enneapogon,and Uniola were selected for comparative chloroplast genomics study,and species from eight genera of Eragrostis,Harpachne,Enneapogon,Uniola,Triraphis,Neyraudia,Centropodia,and Danthoniatriaphis were selected for phylogenetic analysis.Based on the morphology and molecular phylogeny,The morphological characteristics,intergeneric and interspecific relationships,and phylogenetic relationships of Chinese Eragrostideae were discussed.The results of this study are as follows:(1)The lower epidermis of leaves and caryopsis of the selected species were observed by scanning electron microscope and anatomical lens.A total of five micro morphologies of lower epidermis of leaves(undulations of epidermal long cell,shape of phytolith,shape of stomatal subsidiary cells,micro-hairs type,macro-hairs),and seven micro morphologies of caryopsis(fruit length,fruit color,solid figure,ventral face,hila shape,mode of caryopsis compression,embryo proportion)were selected for carrying out Q-type cluster analysis and preliminary studying the genetic relationships of each species in Eragrostideae.The results showed that the18 species of Eragrostideae can be divided into two groups at the squared Euclidean distance of20.The first group was divided into a single branch of Enneapogon desvauxii.The main characteristics were as follows: the phytoliths on the veins of the lower epidermis of the leaves were dumbbell-shaped,micro-hairs were Enneapogonoid-type,the mode of caryopsis compression was dorsiventral flattened,the embryo proportion was large;In the second category,16 species of Eragrostis were clustered together,among which Harpachne harpachnoides was embedded inside Eragrostis.This phenomenon is consistent with the conclusion reached by many botanists using molecular evidence.(2)Based on the Illumina Hi Seq technology,the second-generation sequencing of 17 species of Chinese Eragrostideae(15 species of Eragrostis,Enneapogon desvauxii,and Harpachne harpachnoides)were carried out to obtain the complete chloroplast genome sequences.Combined with the downloaded sequences,a total of 24 chloroplast genomes of Eragrostideae were collected.Bioinformatics analysis showed that the size,structure and gene composition of the chloroplast genomes were relatively conservative.The size of the chloroplast genomes of Eragrostideae is about 134 kb,which encodes 129-133 genes,including 83-87protein-coding genes,38 t RNA genes,and eight r RNA genes.The GC content are 38%.The codon usage of Eragrostideae is coincident,and the codon ending with A/T base is preferred.The number and type of repeats in the chloroplast genomes of Eragrostideae are also coincident.The chloroplast genome sequences of Eragrostideae were analyzed by sequence alignment.The result showed that chloroplast genomes were highly conserved.The IR region contraction and expansion analysis also showed IR region were different but also highly conserved.(3)Similar topological structures were observed in the maximum likelihood trees of 24 species in Eragrostideae based on four data sets(complete chloroplast genomes,coding sequences,non-coding sequences,hypervariable regions).Phylogenetic analysis found that Eragrostideae was divided into three main clades.Among them,the three species of Enneapogon formed a monophyletic branch,corresponding to Cotteinae,which differentiated first.One species of Uniola gathered into a clade,corresponding to Unioliinae.Eragrostis and Harpachne were clustered into a large branch,corresponding to Eragrostidinae;Unioliinae and Eragrostidinae are more closely related.In addition,the interspecific relationship of Eragrostis has also been well resolved.Based on morphological and molecular evidences,this study suggested that Harpachne harpachnoides should be an evolutionary group of Eragrostis.This is the first time that the complete chloroplast genomes support the clustering of Harpachne into Eragrostis.In this study,morphological analysis and molecular phylogenetic studies of Eragrostideae species distributed in China were conducted.The results provided new evidence for the reconstructing the phylogenetic relationship of Eragrostideae species.The phylogenetic problems of Eragrostideae can be solved by broad sampling and using complete chloroplast genomes data. |
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