Mechanisms Of HaDV2 Promoting The Development Of Larval Helicoverpa Armigera

Helicoverpa armigera is an important agronomic pest, and it can cause huge economic losses every year. Densovirus is a parvovirus which parasitizes in the invertebrates specifically, and most of them are high lethal for their host. Previous studies have shown that the HaDV2, a novel densovirus in the H.armigera, can increase the egg production and the offspring, shorten the larval development time, improve the larval survival rate and extend the lifespan of females. Furthermore, it can improve the resistance to the HaNPV in the H.armigera. In order to understand the mechanisms of HaDV2 promoting development of larval H.armigera, the paper analysed the transcriptome of the larve infected DV after 24 h, 48 h and 72 h, and we measured the change of juvenile hormone titer and digestive enzymes activity of the samples. The main findings are as follows:1. We found 306 differentially expressed genes(DEGs) in the transcriptom of all samples, and 77 genes expression were up-regulated, 229 genes expression were down-regulated. There are 3 significant difference genes in all samples. The enrichment analysis of KEGG pathway showed that there were 16 pathways which were significant enrichment, and the number of gene in the starch and sucrose metabolism is the maximum. Lots of DEGs were related to the biological characteristics, such as enzyme activity, immune defence, hormones level, high infection rate of virus, more eggs and long life span.2. There were 170 DEGs in the transcriptom of 24 h samples, and 41 genes expression were up-regulated, 129 genes expression were down-regulated. The enrichment analysis of KEGG pathway showed that there were 5 pathways which were significant enrichment, and the number of DEG in the insulin signal pathway was the maximum. Lots of DEGs were related to the biological characteristics, such as enzyme activity, hormones level, immune defence, high infection rate of virus, more eggs and long life span.3. There were 228 DEGs in the transcriptom of 48 h samples, and 67 genes expression were up-regulated, 161 genes expression were down-regulated. The enrichment analysis of KEGG pathway showed that there were 10 pathways which were significant enrichment, and the number of DEG in the metabolism of xenobiotics by cytochrome P450, fatty acid metabolism and AMPK signaling pathway is the maximum. Lots of DEGs were related to the biological characteristics, such as enzyme activity, hormones level, immune defence, rapid development of larve. Compared with the DEGs of 24 h, there is no DEGs related to the high infection rate of virus, but DEGs related to the Cannibalism were found.4. We found 528 DEGs in the transcriptom of 72 h samples, and 168 genes expression were up-regulated, 360 genes expression were down-regulated. The enrichment analysis of KEGG pathway shown that, there were 29 pathways were significant enrichment, and the number of DEG in the AMPK signaling pathway is the maximum. Lots of DEGs were related to the biological characteristics, such as enzyme activity, hormones level, immune defence, rapid development of larve, more eggs and long life span. However, the FPKM value of gene related to the long life span was opposite to the above result, which is down-regulated.5. We analysed the effects of HaDV2 on the juvenile hormone titer in larval H.armigera. JH titer reduced with the development of instar, and as for larva on the same day age, JH titer was negative correlated to the weight, the greater weight, the lower titer of JH. The JH titer in non-infected larva was higher than the infected larva, but the difference between two treatments was not significant.6. We analysed the effects of HaDV2 on the digestive enzyme activity. The results of enzyme activities in the infected larva after 24 h, 48 h and 72 h showed that the proteinase activity reduced with the development of larva. Besides, it was higher in the infected larva than the non-infected, but the difference was not significant except for samples infected after 24 h. The trysin activity was higher in the infected larva than non-infected larva, and in addition to 48 h, the enzyme activity on the rest of time point has significant difference, and it increased with the development in the infected larva, but it increased at first and then decreased in the non-infected larva. The chymotrypsin activity decreased with the development of the larva, but the effect of HaDV2 on its activity was not regulated. It was higher in the infected larva than non-infected larva on 48 h, but it was opposite for the rest of time point, and the differences were not significant.In conclusion, HaDV2 infection promoted the larval weight by changing the enzyme activity, up-regulating trypsin gene, down-regulating the lipase and serine protease. Moreover, HaDV2 infection could up-regulate the juvenile hormone epoxide hydrolase and down-regulate juvenile hormone acid methyltransferase. The JH titer would decrease with the influence of the above two factors, and then accelerate the development of larval H. armigera.