The Circadian Entrainment And Photo-transduction Pathways Involved In Signaling During Baculovirus Induced Behavior Changes In Lepidopteran Larvae

The research focuses on the molecular mechanism behind the behavior manipulation in lepidopteran larvae by their pathogenic baculovirus.The transcriptomic study was carried out for Lymantria dispar asiatica third instar larvae infected with L.dispar multiple nucleopolyhedroviruses(Ld MNPV)during hyperactive and tree-top disease stage.The results showed that the coordinated mechanism of Neuroactive ligand-receptor interaction with other functional gene sets plays a central role to bring about the hyperactivity in the host organism.Interestingly,all the genes differentially regulated in Neuroactive-ligand receptor interaction were serine protease.A similar transcriptomic approach has been used to study the genetic changes in L.dispar third instar larvae during tree-top disease.Map visualization for enrichment analysis of significant gene sets grouped based on functional annotation similarity from the transcriptome study revealed circadian entrainment and photo-transduction as the main pathways involved in signaling during tree top disease of L.dispar.The expression pattern of core circadian genes(per and tim)over the course of 24-hours changed significantly from pre-symptomatic phase to tree-top disease stage leading to phase advance in the host insect at the later stage.The RT-PCR results confirmed this pathway involving in treetop disease induction.Directed light bioassay further demonstrated the positively phototactic larvae during tree top disease.Further,the effect of the different wavelength of lights on photo-movement during tree top disease has been observed.The responses of third instar Helicoverpa armigera larvae infected by wild-type Hear NPV to white,blue,UVA and UVB lights during tree top disease stage were determined by bioassay in lab condition.The result suggested that tree-top is induced only when the light is applied from above.Blue light,white light and UVA light from above induce tree-top disease,causing infected larvae to die in an elevated position compared to those larvae in complete dark.In contrast UVB from above does not induce tree top disease.Blue light exerted the maximum photo-tactic response,significantly(P<0.01)higher than white light.The magnitude of the response decreased with decreasing wavelength to UVA and no response at UVB.In conclusion,the pathway study for tree top disease in L.dispar third instar larvae infected with Ld MNPV is primarily triggered by circadian entrainment and photo-transduction mechanism,and the spectral wavelength of blue light is the most sensitive light for tree-top disease as found in Hear NPV infected H.armigera.