| Honeybee sacbrood caused by sacbrood virus(SBV)seriously threatens the survival of honeybee.It can be infected in larval stage,pupa stage and adult bee stage of honeybee.The virus has highly contagious,it can not only infect the Apis cerana,but also proliferate and reproduce in the Apis mellifera,However,its damage to Apis cerana is far more serious than that of Apis mellifera.In order to find out the mechanism of sensitivity and pathogenicity difference between the two species of honeybee to SBV infection.In this experiment,the 2-day old larvae and newly adult honeybee of Apis cerana and Apis mellifera were fed with SBV respectively,the weight,development period and mortality of larvae infected with SBV and the change of weight and survival rate of adult honeybee infected with SBV were studied.It turned out that none of the larvae infected with SBV can normalize the pupa and died all;the larvae weight of infected Apis mellifera decreased significantly(P<0.001)and 12% of them were able to pass through the pupation stage,but the prepupal period was prolonged by 1.5 d;the body weight of adult honeybee significantly decreased(P<0.05)and there was no significant difference in mortality(P>0.05)after feeding the virus for 5 days.The results showed that SBV mainly caused harm to larvae of honeybee,and its fatality to larvae of Apis cerana was higher than that of larvae of Apis mellifera.qPCR was used to detect the expression level of metamorphosis,nutritional metabolism and immunity related genes in 4-day old?7-day old larvae and 10-day old?20-day old adult honeybee.We found that compared with the normal group,the nutritional metabolism related genes,ilp1,hex110,hex70 c,hex70b were significantly down-regulated(P>0.05),the immune genes,apidaecin,defensin,hymenoptaec were significantly upregulated(P>0.05)in 4-day old larvae of Apis cerana inoculated SBV,and the expression of nutrition,immunity and metamorphosis genes had not significant difference in 7-day old prepupae(P>0.05);the 4-day old larvae of Apis mellifera showed that the nutritional metabolism genes were upregulated and the immune genes were down-regulated(P<0.05).7-day old prepupa showed nutrition genes(vg,mrjp1,mrjp3,mrjp5,mtor)?immunity genes(imd,stat92 e,apidaecin,abaecin,hymenoptaecin)and metamorphosis genes(ftz-f1,ecr-a/b,ecr,dpp,usp,brc)were significantly up-regulated(P<0.05).The antiviral genes(loc409544,dicer,key,stat92e)in 10-day old nurse honeybee fed with SBV were significantly up-regulated,while the immune-related genes(pgrp-lc,tak1,traf6)of Apis mellifera were significantly down-regulated(P<0.05);for 20-day old foragers,immune-related gene toll was significantly down-regulated in Apis cerana,immune-related gene ago was significantly down-regulated in Apis mellifera.Therefor,SBV had different effects on the expression of metamorphosis,nutritional metabolism and immunity related genes in the larvae and adult stage between Apis mellifera and Apis cerana.The high expression of apoptosis-related genes in the metamorphosis larvae stage of Apis cerana may be the cause of death.But during this period,Apis mellifera increased the expression of metamorphosis,nutrition and immunity related genes,and survived for a longer time or even successfully pupated.Rack1 is a highly conserved ribosomal protein,a common potential antiviral target.In this study,first,the dsRNA of Rack1 was injected to Apis mellifera and Apis cerana as experimental group,while the control group was injected with dsRNA of eGFP,and the blank group was injected with sterile water.Each bee after injection was then inoculated with SBV.qPCR was used to detect the relative expression of Rack1 and SBV titer in honeybee at 48 h and 72 h after injection.The results showed that the expression of Rack1 in treatment group of Apis mellifera was over 50% less than that of in eGFP group and blank group at 48 h after injection(P<0.05),SBV titer was also 50% lower than that of in control group and blank group(P<0.05).The expression of Rack1 in treatment group of Apis cerana after 48 h was 70% lower than that of control group and blank group(P<0.05),and SBV titer was also reduced by 50%,but no significant difference(P>0.05).After 72 h,the expression of Rack1 returned to normal in Apis mellifera,and the content of SBV was significantly up-regulated compared with that of the experiment group at 48 h(P<0.05),and there was no difference with the control group of the same old(P>0.05).These results suggest that Rack1 does promote the replication and proliferation of SBV in host,which provides a new therapeutic direction and method for the study of sacbrood honeybee. |
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