Genome Size And Repeat Sequence Analysis Of The Chinese Sword-horned Locust And Short-fronted Locust

Most evidence suggests that transposons proliferation is an important driver for genome size variation in arthropods.In insects,whole genome sequencing results showed a strong positive correlation between genome size and the number of transposable elements.The Orthoptera,which is the Order of genomic enlargement in the Insecta,provides an excellent materials for the study of mechanisms of genome size variation.However,due to the lack of data,few systematic studies have been conducted on the characteristics of Orthoptera genome size and repeat composition.Acrida cinerea(Orthoptera:Acrididae)and Atractomorpha sinensis(Orthoptera:Pyrgomorphidae)are kinds of grasshoppers widely distributed in China.At present,the research of the two species is mainly focused on the aspects of morphology,mitochondrial genome and transcriptomics.However,up to now,there have been no reports on the genomes size,content,type and chromosome location of the repetitive sequence of A.cinerea and A.sinensis.Based on the estimation of the genome sizes of the two species,this study was randomLy sequenced using the Next-generation sequencing(NGS)technology to genomic DNA of A.cinerea and A.sinensis.The composition and relative content of repeat sequences of the two species were compared and analyzed with RepeatExplorer.Finally,Fluorescence in situ Hybridization(FISH)techniques were used to analyze the chromosome localization of satellite DNA sequences.The main analysis results are as follows:(1)Estimating the genome size of A.cinerea and A.sinensis.The results of flow cytometry showed that the genome size(internal standard:Locusta migratoria)of the female of A.cinerea was 11.24pg,male was 10.64pg.and the female of A.sinensis was 8.21pg,male was 7.55pg.These species showed significant genomic dimorphism based on sex,which should be due to the sex chromosome determinism mechanism of XO(?)/XX(?).(2)Repetitive sequence analysis of A.cinerea and A.sinensis.The analysis results of NGS sequencing data by RepeatExplorer showed that the content of repeat sequences in the genome of A.cinerea and A.sinensis was 59.54%and 47.77%,respectively.And ten different types of repetitive sequences were detected,including rDNA?satellite?LTR/Bel-Pao?LTR/Ty1_copia?LTR/Ty3_gypsy?Penelope?LINE?Subclass₁/TIR?Subclass₂/Maverick and Subclass₂/Helitron.In A.cinerea,retrotransposon accounted for 34.49%of the genome,among which the most abundant repeats was LINE,accounting for 17.67%of the genome;the content of tandem repeats(including satellite and rDNA)was 5.11%;DNA transposons content were least,accounting for only 2.94%of the genome.In A.sinensis,retrotransposon accounted for 22.77%of the genome;the proportion of LINE reached 12.16%;the content of tandem repeats was 10.10%;DNA transposons also accounted for the least proportion,only 2.01%.(3)Comparative analysis of repetitive sequences between A.cinerea and A.sinensisThe comparative analysis of the repeats between two species showed that only about 1/8 of the clusters represented the shared repeats,and there were some differences in the number of the reads.It mainly contains LINE,Satellite and a small portion of Penelope and 45s_rDNA.Most of the clusters represented repeats specific to individual species,including LTR/Ty3_gypsy and Subclass₂/Maverick.In addition,phylogenetic analysis of the LTR belong to different groups of two species and are assigned to various clades.(4)Chromosomal localization of satellite in A.cinerea and A.sinensis.The FISH results showed that the DNA hybridization sites and distribution on chromosomes of A.cinerea of the two satellites were different.Two probe signals appeared simultaneously on chromosome M4 and M6.The three satellite of A.sinensis in DNA hybridization sites and distribution on chromosomes were also different.All three probe signals appeared on the L1 chromosome,and the satD2 hybridization signal was shown on the X sex chromosome.According to the above results,the following conclusions can be drawn:both of the two species have enlarged genomes,and the content of repetitive sequences in the genomes is relatively high,59.54%and 47.77%,respectively.Flow cytometry,high-throughput sequencing with low-coverage(0.1-0.5×)and FISH were used to reveal the genome size and repeat sequences composition characteristics of the grasshopper genome.