Study On The Function Of Dopamine Signaling Pathway In The "Tree Top Disease" Of Lymantria Dispar

Some parasites manipulate host behavior to enhance transmission.Baculoviruses have been known to induce the infected larvae to climb to the top of their host trees to die,liquefy,and release virus particles.This baculovirus-induced behavior was reffered to as "tree top disease" or “Wipfelkrankheit”.Although there are many attempts to explore the cause of this phenomenon,the mechanism of "tree top disease" has not been clearly defined.In this study,to investigate the molecular mechanism of "tree top disease" by baculovirus infection,the Lymantria dispar larvae infected with Lymantria dispar multiple nucleopolyhedrovirus(LdMNPV)was used as the research object.The role of some genes in dopamine pathway on LdMNPV induced behavioral changes of L.dispar were investigated.At the same time,fungal and viral co-infection of L.dispar was used to explore the effects of co-infection on L.dispar behavior.The main results were as follows:1.The climbing behavior significantly changed after increasing the concentration of exogenous dopamine,and the climbing speed of L.dispar injected with dopamine was significantly higher than the control group.After L.dispar was injected with dopamine inhibitor 3-I-L tyrosine,the climbing speed was significantly lower than the control group.Additionally,the average survival rate of L.dispar larvae declined with increasing dopamine concentration,indicating that dopamine concentration influences larval survival rate.2.For deveploment-specific expression,dopamine-related genes were widely expressed in different development stages.The expression level increases after the third instar larvae,and the expression level was highest in adults.For tissue-specific expression,dopaminerelated genes were expressed in different tissues and were maily expressed in the head and ganglion.3.When dopamine-related genes,tyrosine hydroxylase(TH),dopa decarboxylase(DDC)and dopamine receptor(DD1R),were silenced by RNA interference,the climbing height of L.dispar larvae was significantly lower than control groups after LdMNPV infection.Additonally,there was no siginicant difference in climbing height between the larvae only fed with ds RNA of TH,DDC and DD1 R and those only fed with ds RNA of the Enhanced Green Fluorescent Protein(EGFP)gene.The above results showed that the interference of TH,DDC and DD1 R genes of dopamine pathway could affect the "tree top disease" induced by LdMNPV in L.dispar larvae.4.The climbing behavior of L.dispar larvae infected by fungi and virus was different at different time after combined infection.In the late stage of infection,the climbing speed of L.dispar larvae infected by fungi and LdMNPV was lower than only infected by LdMNPV.At72 h post infection,fungal and viral co-infection resulted in down-regulated expression of dopamine related genes in dopamine pathway,which significantly reduced the climbing height of L.dispar larvae.This result was consistent with the above consequence,when L.dispar.larvae co-infected by fungal and viral,significantly reduced climbing height of L.dispar.These results suggested that dopamine related gene may played an important role in manipulating the behavior of "tree top disease" in L.dispar larvae.It was also found that the mortality of L.dispar larvae increased with increasing fungal concentration,and the death time of larvae was earlier than that infected only with fungi or virus.In conclusion,the dopamine pathway plays a role in LdMNPV-induced "tree top disease".With the increase of exogenous dopamine concentration,the climbing speed of L.dispar accelerated.After silencing the TH,DDC and DD1 R genes in the dopamine pathway,the climbing speed of L.dispar larvae was significantly lower than that of larvae only infected with LdMNPV.In addition,virus-fungal co-infection weakened the "tree top disease" phenotype and down-regulated the expression of dopamine related genes in the dopamine pathway.The further research is reqired to explore the reason for this phenomenon.These results provide new scientific data for clarifying the behavioral regulation of baculovirusinduced lepidopteran larvae.