Multiple Nucleopolyhedroviruses Prevents Pupation of by Regulating Juvenile Hormone Titer.

Baculovirus infection can prevent the pupation of insects. Juvenile hormone (JH) plays a vital role in regulating insect molting and metamorphosis. However, the molecular mechanism of baculovirus preventing the pupation of larvae by regulating the Juvenile hormone (JH) pathway is still unclear. In this study, we found that the multiple nucleopolyhedroviruses (MbMNPV) infection prolonged the larval stage of fourth instar () by 0.52 d and caused an increase in JH titer. To identify the genes that contribute to the JH increase in -MbMNPV interaction, we analyzed mRNA expression profiles of the fat bodies of infected by MbMNPV. A total of 3637 differentially expressed mRNAs (DE-mRNAs) were filtered out through RNA-seq analysis. These DE-mRNAs were mainly enriched in Spliceosome, Ribosome biogenesis in eukaryotes, Aminoacyl-tRNA biosynthesis, Mismatch repair, and RNA degradation signaling pathway, which are related to the virus infection. Real-time PCR was used to verify the RNA sequencing results. To find out which genes caused the increase in JH titer, we analyzed all the DE-mRNAs in the transcriptome and found that the and genes, which were related to JH degradation pathway, were down-regulated. and genes in the larvae of MbMNPV-infected group were significantly down-regulated compared with the control group by RT-qPCR. We further proved that the JH is degraded by JHE in larvae by RNAi, ELISA, RT-qPCR and bioassay, while the hydrolysis of JH by JHEH in larvae can almost be ignored. Knocking down of promoted the expression of the JH receptor gene and the downstream gene , and the replication of MbMNPV. This study clarified that JH is mainly degraded by JHE in larvae. The MbMNPV infection of larvae leads to the increase of JH titer by inhibiting the expression of . The increase in JH titer promotes the expression of the JH receptor gene and the downstream gene , which prevents the pupation of , and promotes MbMNPV replication. This study provides new insights into and MbMNPV interaction mechanisms.