Comparison Of Genome And Insecticidal Activity Of Three Isolates Of Plutella Xylostella Granulovirus

Plutella xylostella granulovirus(PlxyGV)is a member of the Batabaculoviruses,which has great virulence to the Plutella xylostella.PlxyGV pesticides produced for commercial have been put into large-scale application.In order to understand the genetic stability of PlxyGV in natural state,the complete genome sequences and insecticidal activity of three PlxyGV isolates were comparatively analyzed.(1).The genomes of PlxyGV-W(Wuhan strain),PlxyGV-B(Beijing strain)and PlxyGV-WN(New Wuhan strain)were sequenced by using a second-generation sequencing technology.The gaps between the sequence contigs were filled by PCR and first-generation sequencing technology.The genome sizes of PlxyGV-W,PlxyGV-B and PlxyGV-WN were 100941 bp,100972 bp and 100999 bp,respectively.(2).The three PlxyGV isolates,equally contained 118 open reading frames(ORFs)contsisting of>50 codons with minimal overlapping and four homologous repeat regions.There are 330 base mutations between PlxyGV-W and PlxyGV-B genomes,including 98 transitions,60 transversions and 173 insertion/deletions;resulting in 12 non-synonymous mutations in seven ORFs.Six out of the positions with non-synonymous mutations contain sequence polymorphysms(except orf20).There are 730 base mutations between PlxyGV-W and PlxyGV-WN genomes,including 337 transitions,131 transversions and 262 insertion/deletions,inducing 70 non-synonymous mutations in 47 ORFs.12 out of the positions with non-synonymous mutations contain sequence polymorphysms.(3).Comparative analysis of the genome sequences of PlxyGV-W,PlxyGV-B,PlxyGV-WN and six additional reported PlxyGV isolates showed that the identities of genome sequences between PlxyGV-W and PlxyGV-B and PlxyGV-WN were 99.67%and 99.28%,respectively.Except for PlxyGV-SA,the identities between the genomes of the other PlxyGV isolates were over 99%.Sequence identities between PlxyGV-SA and the other PlxyGV isolates were 98.20-98.53%.Except for PlxyGV-J,the genomes of the other eight isolates contained the same number of ORFs(118).Fifteen ORFs are unique to PlxyGV.(4).To determine the transcription satart sites and the polyadenylation sites of the PlxyGV-specific genes,total RNAs of Plutella xylostella larvae infected by PlxyGV-WN were extracted.5’-RACE analysis of the transcripts from eleven PlxyGV-specific ORFs,The result showed that ORF56 and ORF109 had two transcription satart sites,ORF27 had three transcription satart sites,and while the other ORFs had single ones.3’-RACE analysis showed that all the fifteen PlxyGV-specific ORFs had single polyadenylation sites.(5).The results of bioassay of three PlxyGV isolates on the Plutella xylostella larvae showed that the median lethal concentration of PlxyGV-W,PlxyGV-B and PlxyGV-WN were 1.695-2.300×107 OB/mL、1.570-2.375×107 OB/mL and 3.131-5.038×107 OB/mL,respectively.The difference between PlxyGV-W and PlxyGV-B was not significant,while the difference between PlxyGV-WN and PlxyGV-W and PlxyGV-B was significant.The survival times of the second instar Plutella xylostella larvae infected by PlxyGV-W,PlxyGV-B and PlxyGV-WN at a concentration of 1×109 PIB/ml were all about 120 hours,without significant difference.