| The interactions among plants,herbivores and insect viruses are one of the focus in ecology and entomology.We used host plants,beet armyworm and Se MNPV as the research objects,to discuss following issues: 1)effects of phytochemicals on virus lethal insects;2)how plants regulate the effects of the virus infection on the structure of midgut and peritrophic membrane,and the amount of midgut genes expression.The main results are as follows:1.To explore the ecological effect of plants on insect-virus interactions,the susceptibility of 3 species of plant and artificial feed(control)to the virus was tested by the leaf disc method,and the disease and death of the larvae infected with different food resources were analyzed.The results showed that the food resources,the dose of virus and their interaction effect significantly affected the mortality and survival time,and the mortality of larvae decreased with the prolongation of survival time;infected larvae feeding on Ipomoea aquatica leaves have the LD50(1222.4 OBs/ larvae),and the ones feeding on Glycine max and artificial diets were 110.5,107.6 OBs/larvae both of which have no different significance.The results of exponential model simulation showed that the LD50 increased with the increase of total phenol content and peroxidase(POD)activity in leaves,but decreased with the values of the other 4 enzyme activity.This study reveals that after feeding Glycine max,virus disease of Spodoptera exigua is strongest and after feeding Ipomoea aquatica is the weakest;Total phenol and peroxidase in the inhibition of plant leaf virus disease of beet armyworm,and catalase(CAT),superoxide dismutase(SOD),endochitinase,and exo-chitinase increase it.2.To elucidate the physiological effects of host plants on virus-infected host,the changes of peritrophic membrane(PM)in Spodoptera exigua at different time points were observed by asana microscope.And we used paraffin sectioning technology to investigate the pathological changes in the midgut tissues,which feed on 3 plants and artificial feeds.The results showed that the structure of PM of infected larvae feeding on any food was changed from transparent and flexibly cylindrical structure to opalescent and sheet-like structure with reduced elasticity,the degree of damage of the PM increased with the increase of virus treatment time.When the larvae were infected,the destroy of virus to the midgut was greatest on artificial diets or Glycine max,the following was Brassica oleracea and the least damage was on Ipomoea aquatica.This study suggests that host plants can affect virus destroy the midgut tissues.3.To further testify the physiological effects of host plants on virus-infected host,we extracted the PM of beet armyworm larvae feeding on 3 plants and artificial diets,observed the ultrastructure of PM by using electron microscope scanning,and selected 7 observation time points(exposure time of 1,2,3,6,12,24 and 48 h after NPV treatment).The results indicated that the PM of the infected larvae feeding on artificial diets appeared to be holes on 1 h after treatment,recovered(no holes)on 2 h,and were destroyed gradually from 3 h after treatment;the PM of infected larvae feeding on Glycine max was gradually destroyed from 1 to 2 h after treatment,the degree of destruction is reduced on 3 h,and were also destroyed gradually from hour 6 to 12 after treatment;after the larvae fed on Brassica oleracea,the PM of the infected larvae was damaged gradually in the first 3 h,and 6 h was decreased,but this damage was aggravated gradually from 12 h;after the larvae fed on Ipomoea aquatica,the PM of the infected larvae was damaged gradually in the first 6 h,12 h was decreased,and 24 h become serious.In addition,it was also found that 24 h and 48 h after infection,the PM holes of feeding artificial diets were the largest,and the order of eating Glycine max,Brassica oleracea and Ipomoea aquatica weakened.After the infection of larva by feeding artificial diets,Glycine max,Brassica oleracea and Ipomoea aquatica,the time points for the holes appearing on the PM of the larvae were 1,2,2 and 3 h,and recovered was 2,3,6,12 h.Thus,we concluded that host plants could regulate the effects on the PM of infected larvae.4.To reveal the molecular effects of host plants on virus-infected host,we constructed 48 h D(virus-infected)and 48 h W(non-infected)transcriptome libraries of beet armyworm,using the Illumina Hi Seq sequencing platform have access to the Clean Reads of 48 h D and 48 h W were 4.346 x 107 and 4.248 x 107,accounting for 98.65 and 98.66% of the Raw Reads.We got 74066 unigenes,of which 3265 unigenes shared annotation with 5 databases,including NR,GO,KEGG,Egg NOG and Swissprot.There were 11584 unigenes annotate to GO,and the 243 unigenes participated in the immune system process.The 5526 unigenes were annotated by KEGG,participated in the gene sequences of cell growth and death,and the immune system in KEGG metabolism were 214 and 195 respectively.Through differential gene expression analysis,we found that there were 1785 differetially expressed genes(DEGs)between 48 h D and 48 h W,and the number of up-regulated and down-regulated genes were 935 and 850 respectively.5.Spodoptera exigua feeding on artificial diets,Glycine max,Brassica oleracea and Ipomoea aquatica were at 4 h and 12 h after being infected,the expression of Spodoptera exigua insect intestinal mucin(Se IM)gene in the Glycine max group was significantly higher than that in the other 3 groups,while there were no significant difference in the expression level of Spodoptera exigua chitinase(Se CS)at 4 h after being infected.After 12 h,the expression level of Se IM feeding artificial diets was significantly higher than that in Brassica oleracea and Ipomoea aquatica groups,and the expression level of Se CS feeding artificial diets was significantly higher than other 3 groups.After 24 h,the expression levels of Se IM and Se CS feeding artificial diets and Glycine max were significantly lower than those in Brassica oleracea and Ipomoea aquatica groups.After 48 h,the expression level of Se CS feeding Brassica oleracea and Ipomoea aquatica groups were significantly higher than that of the other 2 groups.Based on the tritrophic interactions of plants,beet armyworm and Se MNPV,we expounded the plant-mediated effects of the infectivity of Se MNPV to beet armyworm.These results concluded that host plants could regulate the infectivity of Se MNPV to beet armyworm,and that this difference of infectivity on different plants could guide the practice of agricultural production,which has a great significance for the effective use of insect viruses to control pests on different crops.In addition,this study found that the Se MNPV infection has the potential to alter the midgut and PM structure,and the gene expression.These conclusions will enrich the physiological and molecular mechanisms that plant cooperated with insect virus to defend against insect herbivores. |
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