Virome Analysis And New Virus Identification Of Small Brown Planthopper (Laodelphax Striatellus)

Small brown planthooper(SBPH,Laodelphax striatellus;Hemiptera: Delphacidae),which distributes throughout east Asia,southeast Asia,Europe,and north Africa,and all over China,is one of important sap-sucking pests.Except causing damage to host plants especially in high density by sucking the sap,SBPH can lead to more significant yield losses at a much lower density by transmitting numerous viruses such as rice stripe virus(RSV),rice black-streaked dwarf virus(RBSDV),maize rough dwarf virus(MRDV),northern cereal mosaic virus(NCMV)and barley yellow striate mosaic virus(BYSMV)that cause serious diseases on staple crops.In previous studies,well-known about its biological and transmission characteristics,but only limited information about its commensal viruses.In this paper,we conducted a comprehensive study on its commensal viruses in the populations collected from16 regions of China by transcriptome sequencing.Six viruses were identified by sequence assembly and alignment,including three known viruses: Himetobi P virus(HiPV),Laodelphax striatellus iflavirus 1(LsIV1)and Laodelphax striatellus associated partitivirus(LsaPV),and three unknown viruses,tentatively named as Laodelphax striatellus Fiji-like virus,Laodelphax striatellus Phle-like virus and Laodelphax striatellus Virga-like virus.On the basic of RT-PCR detection,we compared and analyzed the distribution of different virus species in each region.The results showed that Laodelphax striatellus Virga-like virus was the most widely distributed one,covering 16 regions,followed by Laodelphax striatellus Phle-likevirus,HiPV and LsIV1,while Laodelphax striatellus Fiji-like virus and LsaPV had low detection rates.In addition,there were some differences in the virus species and detection rates among different regions,but also have some common rules.Four virus species were found in the SBPHs collected from Yuanyang of Henan Province,Huaian of Jiangsu Province and Hefei of Anhui Province,all belong to central and eastern regions of China,but only one to three virus species in other regions of China.Phylogenetic tree analysis based on the RNA dependent RNA polymerase(RdRp)and capsid protein(CP)showed that the HiPV-CP sequence isolated from Yangzhou and Yuanyang was the most similar to the original sequence,while that from Jinan and Zaozhuang were far apart.The LsIV1-RdRp isolated from Dezhou is the closest to the original sequence.The LsaPV-RdRp gene isolated from Yuanyang,Henan Province was the closest to the original sequence,followed by that of Beijing.For the three unknown viruses,the RdRp sequences of Laodelphax striatellus Phle-likevirus isolated from Beijing and Wuhan were the closest in evolutionary relation,followed by those of Tangxian,Changsha and Yangzhou.The RdRp sequences of Laodelphax striatellus Fiji-like virus isolated from Hefei and Kunming have the closest evolutionary relationship.The sequences of Laodelphax striatellus Virga-like virus are highly conserved,i.e.,almost no mutations in different regions.We also performed preliminary recombination,polymorphism and single nucleotide polymorphism(SNP)analysis of six viral genomes based on sequencing data and bioinformatics.In addition,we also identified a new virus in leafhoppers using high-throughput sequencing.Summary,this study conducted on virome of SBPH populations collected in different regions of China.Except three new viruses have been identified,the distribution,genetic variation,and system evolution characteristics of SBPH commensal viruses have also been studied.Our results would provide a theoretical basis knowledge of insect commensal viruses.