| Induced defense and constitutive defense are important ways of plant defense.Plants initiate defense systems to suppress pest populations by activating various defense pathways.It has been found that Beauveria bassiana,as an entomopathogenic fungus,acted as an endophytic fungus to stimulate the defense system of plants.However,little is known about whether colonization of B.bassiana affected the metabolic pathways involved in producing plant secondary metabolites,the potential influence of plant secondary metabolites on pests,and the related physiological mechanism.In this study,B.bassiana(Bb252),Bemisia tabaci(MED)and tomato(Solanum lycopersicum)were employed to explore the underlying mechanisms by which B.bassiana as endophytic fungi induced defenses of tomato to pest.The main results are as follows:1.B.bassiana activated phenylpropanoid metabolic pathway in tomatoes.The expression levels of genes in phenylpropanoid metabolic pathway in tomatoes were determined after the colonization of B.bassiana.The results showed that the genes of phenylpropanoid metabolic pathway in tomatoes were up regulated after 3 days of inoculation.After 7 days of inoculation,the number of up-regulated genes were the highest.Among them,PAL,C4 H,and FLS were up regulated throughout this study.After 7 days of inoculation,PAL gene,CHS gene and FLS gene were up regulated by 16.45,7.93,7.93 times respectively and reached their peak.These genes mainly involved in the metabolic pathways of secondary plant metabolites.After clarifying the up-regulated expression of phenylpropanoid metabolic pathway genes in tomatoes induced by B.bassiana,the potential effects of B.bassiana on the contents of plant secondary metabolites of tomatoes were detected.The results showed that tannin,anthocyanin and flavonoid content in tomato leaves significantly increased at 3 d,7d and 14 d after inoculation by B.bassiana.The content of tannin,flavonoid and Anthocyanin significantly increased at 7 days after inoculation,were 2.02 times,2.07 times and 2.92 times of that in untreated plants.The results indicated that under the induction of B.bassiana,plants enhanced their production of plant secondary metabolites.2.Effects of plant secondary metabolites on the survival and reproduction of B.tabaciThe daily fecundity and total fecundity of B.tabaci decreased after feeding on artificial diets with different concentrations of plant secondary metabolites.The total oviposition rate of B.tabaci fed on artificial diet with 3 mg/kg tannin,4 mg/kg tannin,4.5 mg/g anthocyanin and 70 mg/g flavonoid were decreased by 14%,19%,16% and 12% compared with that of control,respectively.Overall,plant secondary metabolites significantly decreased the reproduction of B.tabaci.It was found that the survival rate of B.tabaci after feeding on different concentrations of plant secondary metabolites was lower than that of the control,but there was no significant difference.However,the developmental duration of B.tabaci after feeding on plant secondary metabolites is prolonged.The developmental durations of whiteflies fed on artificial diet with 70 mg/g flavonoid and 4.5 mg/g anthocyanin were significantly prolonged to 24.05 ± 1.36 d and 23.70 ± 1.78 d,respectively.3.The effects of plant secondary metabolites on digestive ability and detoxification metabolism of B.tabaciAfter clarifying the effect of plant defense response on the reproduction and survival of B.tabaci,the effects of plant secondary metabolites on the digestion and detoxification of B.tabaci were evaluated.The genes of B.tabaci involved in digestion showed an immediate down-regulated trend.The genes such as sucrase,amylase and protease remained low expression.With the prolongation of feeding time,the fold change of down-regulated genes increased.The activities of digestion enzymes in B.tabaci including amylase,trypsin and sucrase all decreased.It was confirmed that the digestive enzyme activity in B.tabaci was inhibited by plant secondary metabolites,which may reduce the digestive capacity of B.tabaci and result in insufficient nutritional for the development and reproduction of B.tabaci.After feeding on artificial diets containing different concentrations of plant secondary metabolites,the detoxification genes of B.tabaci showed an up-regulated expression trend in the early stage of feeding,and the expression of these genes then decreased with the prolongation of feeding time.The activities of detoxification-related enzymes in B.tabaci were increased after feeding on plant secondary metabolites.It proved that plant secondary metabolites were harmful to B.tabaci.The expression level of detoxification metabolism genes of B.tabaci decreased when B.tabaci fed on plant secondary metabolites for a long time.In conclusion,compared with plants not inoculated with B.bassiana,plants colonized with B.bassiana can initiate their defense to agricultural pests by destroying the digestive system and detoxification metabolic system of pests and further the adversely influencing their growth and reproduction.These results provided theoretical foundation to employ B.bassiana as an exogenous stimulant to induce agricultural crops to prevent and control agricultural pests.This study also contributed to our understanding on the fungi-plant-pest interactions. |
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