Characterization of genome repeat sequence composition and chromosomal distribution in Leymus secalinus
[Objective]Leymus Hochst.stands as a crucial genetic resource for the genetic improvement and breeding of cereal crops.However,as allopolyploid plants,their genome origin remains unclear.This study aims to explore the genomic origin of the species in Leymus secalinus and the characteristics of inter-species genomic diversity by comparing the distribution of the repetitive sequences in the genomes of L.secalinus,L.racemosus,and Psathyrostachys juncea.[Methods]Genomic Cot-1DNA library of L.seca-linus was constructed,and clones were sequenced and analyzed.The repetitive sequences were mapped to the chromosome of L.secalinus,L.racemosus,and P.juncea by fluorescence in situ hybridization(FISH).[Results](1)The repetitive sequences of the Cot-1 DNA of L.secalinus were classified into 4 types based on their expected genomic distribution patterns:Tandem repeats,dispersed repeats,tandem mixed dispersed repeats,and uncharacterized repeats,representing 32.4％,45.7％,12.4％,and 9.5％,re-spectively.(2)The number of the hybridization sites of the tandem repeats TaiI-family,Lt1-6,pTa-535,and pSc250 were highly varied from 7-20,1-14,17-26,and 0-24,respectively,across different spe-cies and accessions.(3)Ten LTR repeats hybridized the tested species chromosomes mainly by 3 patterns.Hybridizations were distributed in centromere,pericentromere,and intercalary regions in all chromo-somes.Hybridizations were distributed in all the chromosomes.Hybridizations were distributed the same as the pattern 1 except some chromosomes were carrying telomeric hybridizations.Two LTR/copia se-quences were detected only in L.secalinus,while the others were detected in all species and accessions tested but with polymorphisms in hybridization intensities or hybridization patterns in partial chromo-somes.[Conclusion]Some of the repetitive sequences in Leymus species may have the characteristics of rapid evolution,which supports the rapid homogenization spread of scattered repetitive sequences to the entire nuclear genome during the polyploidy of Leymus species.
Leymusrepetitive sequencesfluorescence in situ hybridization(FISH)polyploid
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