Analysis Of MpnDV Genome Structure And The Effect On Growth Of Myzus Persicae Nicotianae

Myzus persicae can cause large economic losses by destroying leaves and spreading plant virus among many crops.We identified a new densovirus MpnDV in aphids?Myzus persicae nicotianae densovirus?;densoviruses belong to the subfamily Densovirinae within the family Parvoviridae.This virus was a small?18–26 nm in diameter?,single-stranded DNA virus.Densoviruses?DVs?are found in many organisms;the relationships between the virus and host are diverse and DVs are generally pathogenic to their hosts.However,some are beneficial and co-evolutionary relationships have recently been reported.As early as 2003,van Munster detected Myzus persicae densovirus in peach aphid.To determine the effect of MpnDV on the growth of Myzus persicae nicotianae,we amplified the whole genome sequence for comparison with the MpDV genome,and then performed random amplification of cDNA ends?RACE?to obtain the 3?and 5?ends of the sequence for transcription analysis.Second,the infection rate of MpnDV was detected in 29 regions,on the basis of partial nonstructural protein?NS?and capsid protein?VP?gene sequences in samples from 10 locations in China,in an attempt to determine MpnDV genetic variation.Finally,using a life table to analyze the influence of MpnDV on aphid growth and reproduction,the following findings were obtained:?1?Analysis of MpnDV genome structure:The genomic sequence of MpnDV was 5480 base pairs in length and possesses an ambisense genome.The gene encoding NS and VP were distributed in two complementary strands.However,MpnDV isolated from M.persicae nicotianae differed from MpDV in the number and length of open reading frames?ORFs?.MpnDV contains four ORFs,two of which encode NS proteins and two of which encode VP proteins.The initiation and termination sites of NS and VP also differed.Alignment analysis indicated that MpnDV showed 97%sequence identity with MpDV,and the shortened ORFs resulted from nucleotide indels,suggesting that MpnDV and MpDV are two isolates of the same virus.?2?Transcription of MpnDV:By mapping the viral transcripts by RACE,we determined the genome organization of MpnDV.The results suggested that the NS2 ORF of MpnDV was located in the NS1 ORF.MpnDV has a unique genome structure.Its VP protein is encoded by one ORF and contains two introns.?3?Genetic variability of Myzus persicae nicotianae densovirus,based on partial NS and VP gene sequences:MpnDV is widely distributed in wild populations of M.persicae nicotianae?34%in 622samples?,and the infection rate was found to exceed 75%in eight of the 29 locations.The F_ST?0.832?and Nm?0.05?of MpnDV showed low gene flow and high genetic diversity,suggesting that the virus is vertically transmitted and that endosymbiotic viruses can be used as markers in studies of insect population genetics.?4?The effect of MpnDV on Myzus persicae nicotianae growth,development,and fecundity:The life tables of parent and offspring were measured.MpnDV-infected nymphs required less time to reach maturity than healthy nymphs.MpnDV-infected aphids had shorter lifespans than MpnDV-free aphids.The number of daughters produced was significantly increased in the infected group;the offspring showed the same trend.These results suggest that a symbiotic relationship exists between MpnDV and aphids.The two generations of life tables showed that the impact of MpnDV on offspring was weakened.In conclusion,we identified a new densovirus in Myzus persicae nicotianae,although it clustered with the genus Ambidensovirus.MpnDV may promote development and improve fertility of Myzus persicae nicotianae.A symbiotic relationship exists between aphids and MpnDV.Phyletic evolution between the mutualistic virus and host is the basis of parsing the host insect adaptability,showing potential for the development of new pest control methods.