Phylogenetic Analysis Of Chloroplast Genome Of The Ns-Containing Species In Triticeae(Poaceae)

Whole-genome duplication,i.e.polyploidization,is a significant driving force for the evolution of organisms and the main way for plants to adapt to the natural environment.Tracing the ancestors of polyploid species is of great significance for understanding how these species originated and how they have evolved after their origin.It also provides theoretical guidance for further improving the protection and utilization of plant germplasm resources.The chloroplast genome is widely used in plant phylogenetic inference,understanding the process of plant species formation and differentiation characteristics due to its low incidence of recombination events within the genome,small effective population size,maternal inheritance and other characteristics.At the same time,the genes in the chloroplast genome will undergo adaptive evolution and generate new phenotypic characteristics,which is conducive to the diversity of species,and some potential nuclear-cytoplasmic interactions are also conducive to promoting the differentiation of species.This plays an important role in species formation and differentiation,and is suitable for phylogenetic studies in plant taxa and inference of species origin and differentiation.Psathyrostachys Nevski is a very important diploid genus in Triticeae,Leymus Hochst.and Pascopyrum á.L?ve are allopolyploids,they constitute three Genera of Triticeae with Ns genomes,they are the main components of grassland,meadow and desert vegetation in the northern hemisphere,and also the important genetic resources for improving wheat crops.However,there are many species and complex origins of Ns-containing genomes,especially the source of the Xm genome of Leymus and Pascopyrum is unknown.Therefore,phylogenetic analysis of the chloroplast genomes of these three genera containing Ns chromosomes is important to clarify the genetic relationship.In this study,phylogenetic analysis was conducted on complete chloroplast genomes of 7 Psathyrostachys juncea,8 Leymus species,1 Pascopyrum species,33 Triticeae diploid species and 3 Elymus species to explore the intergeneric relationships of three Ns-containing genomes,and the main results were obtained as follows:1.The phylogenetic analysis of the complete chloroplast genome matrix of 52 materials showed that Pascopyrum smithii from North America in the Pascopyrum genus and Elymus sibiricus from Elymus genus were clustered together,indicating that Pascopyrum smithii used the donor species of Elymus St H genome as the maternal donor during the formation of its polyploid species.2.The phylogenetic analysis of the complete chloroplast genome matrix showed that Leymus chinensis,Leymus duthiei,Leymus arenarius,Leymus racemosus and Leymus multicaulis from Eurasia formed polyploid species with Ns chromosome group of Psathyrostachys as maternal donor,while Leymus coreanus and Leymus komarovii from east Asia,and Leymus triticoides from North America used Xm chromosome donor species as the maternal donor during the formation of their polyploid species.This indicates that there is a maternal haplotype polymorphism in the polyploid species containing Ns genome.3.To explore the origin of the Xm genome,we performed coding gene matrix,non-coding region matrix,St / E genome sequence matrix,O genome sequence matrix,W genome sequence matrix,and P genome sequence matrix analysis:(1)analysis of genetic distance and MJ network of coding gene matrix and non-coding region matrix.The results of genetic distance showed that Xm genome is closely related to St / E,O,P,W,F / Xe genome.The results of MJ network showed that the smallest average mutation steps of Xm haplotypes are all St / E,O,W,P haplotypes,indicating that the Xm genome is closely related to the St / E,O,W,P genomes;(2)phylogenetic analysis,MJ network analysis and DNA divergence between populations analysis were carried out for the five genome sequence matrixes of St / E,O,W and P,the phylogenetic trees and complete chloroplast genome matrix phylogenetic trees are almost identical,the results of the MJ network show that the least number of steps with the Xm haplotype mutation are St / E,W,and P haplotype,the analysis results of DNA divergence between populations to a large extent show that the population of Xm genome corresponding to the four genomes of St,E,W and P has the smallest degree of differentiation and the most distant relationship with the Ns genome.The above results show that Xm genome is closely related to St,E,W and P genomes,and it is inferred that the diploid ancestors of Xm genome are extinct,and that the current Xm genome is like a mosaic genome involving four genomes: St,E,W,P.