Establishment Of Chromosome Identification System Of Leymus Chinensis By Multi-color FISH

Leymus chinensis(Trin.)Tzvel is a widely distributed perennial grass species in Leymus genus and an important forage resource in China.L.chinensis not only has important economic and ecological values,but also has a high academic value as the tertiary gene pools of common wheat and naturally evolved polyploid.However,the cytogenetic research and genomic analysis of L.chinensis are relatively lagged.The significant biological information such as genomic structure,genome composition,physical map,and evolutionary relationship is very limited,which seriously hinders the evaluation,protection and utilization of the resources of L.chinensis.Plant chromosome identification technology is an important technical method in plant cytogenetics,especially in species that have not achieved whole genome sequencing,and it can be used for the studies of the evolutionary relationships,phylogenetic developments,and chromosome behaviors among the related species.In this study,the accurate chromosomal identification system of L.chinensis was established by low-coverage genomic sequencing,bioinformatics analysis,multi-color FISH,single copy gene FISH.The relationship between the chromosomal map of L.chinensis and the genetic map of wheat were established,and the nomenclature of L.chinensis chromosomes was unified,and the karyotypes of L.chinensis from different regions were compared.This study promoted our understanding of the genome structure of L.chinensis,and established a modern cytogenetic identification system for L.chinensis,which provides a useful tool for further studying the phylogenetic relationship among L.chinensis and its related species.The main findings are as follows.(1)0.3-fold genome sequences data of L.chinensis was obtained by low-coverage genomic sequencing.Twelve tandem repetitive sequences including CL6,CL95,CL121,CL151,CL162,CL239,5S rDNA,26 S rDNA,and 18 S rDNA sequences etc.were detected by bioinformatics analysis,and were used for cytogenetic studies.(2)The physical locations of the tandem repetitive sequences mentioned-above were identified separately on the chromosomes of L.chinensis by FISH.Then combined with multi-color FISH and two-round hybridizations,the whole chromosome set of L.chinensis was identified.(3)Since the high sequence similarity and gene co-linearity between wheat and L.chinensis,the connection between the physical chromosome map of L.chinensis and the genetic map of wheat were established using wheat chromosome specific single gene probe.Partially homologous chromosomes of L.chinensis were also identified.Combining with the chromosome identification technology developed in this study,the nomenclature of L.chinensis chromosome was unified.(4)The karyotypes of four accessions of L.chinensis from different regions were analyzed using our chromosome identification system.The locations of repeated sequences are not conserved in those accessions and chromosome rearrangements existed in the genome,which suggested that L.chinensis suffered a high chromosome differentiation.