| The green peach aphid,Myzus persicae（Hemiptera:Aphididae）,is one of the most destructive agricultural pests with a worldwide distribution.To date,control of the aphid species is mainly rely on chemical pesticides.However,extensive application of chemical pesticides causes not only environment pollution,but also insecticide resistance in M.persicae.Entomopathogenic fungi have attracted much attention in management of M.persicae since their high pathogenicity to aphids and safety to environment.Most importantly,entomopathogenic fungi are unlikely to cause any insecticide resistance.Lecanicillium includes a family of fungi with high virulence to M.persicae and are of great potential in biological control of aphids.Lecanicillium dimorphum is an important fungal species in Lecanicillium;however,the pathogenicity of L.dimorphum on M.persicae and the defense mechanisms of M.persicae against L.dimorphum are still unknown.In this study,a strain of L.dimorphum was isolated from a naturally infected M.persicae,and the virulence and field efficacy of the fungus against M.persicae were studied.Furthermore,transcriptome sequencing technology was used to analyze the differential expression genes of M.persicae infected with the fungus.Next,the function of thaumatin-like protein genes in defense against fungal infection was determined.The results of this study are as follows:1.Identification of a L.dimorphum strain and evaluation of its pathogenicity and field efficacy against M.persicaeA fungal strain was isolated from a naturally infected M.persicae collected from the field,and was identified as L.dimorphum（designated HFLD1）by using morphological and molecular biological methods.The results of bioassays showed that,with the increase of HFLD1 conidial concentration,the mortality of M.persicae increased.When the concentration was 1×108conidia/m L,the corrected mortality rate reached 95.06%at 7 days after inoculation,and LT50was 3.28 days.After HFLD1 treatment,the fecundity of M.persicae decreased,and the aphid yield was significantly reduced compared with the control group.The results of field trials showed that after treatment with a suspension of1×108conidia/m L for 7 days,the field efficacy of HFLD1 against M.persicae reached79.87%.2.Differential expression genes of M.persicae under HFLD1 infectionThe wingless adults of M.persicae were treated with HFLD1（1×108conidia/m L）,andtranscriptome sequencing was performed to analyzed the differential expression genes.The results showed that a total of 629 genes were up-regulated and 917 genes were down-regulated at 2 days after infection with HFLD1.Among the up-regulated genes,a family of thaumatin-like protein（TLP）genes was found.It is possible that TLPs may play important rolea in defense against fungal infection.3.Functional study of TLPs in protecting against HFLD1 infectionRT-q PCR results showed that four TLP genes（MpTLP1,MpTLP2,MpTLP3 and MpTLP4）were significantly upregulated by HFLD1 infection,confirming the results of transcriptome sequencing.A prokaryotic expression vector was constructed,and recombinant MpTLP2 and MpTLP3 proteins were expressed in Escherichia coli.An optical density-based method was preliminarily established for estimating the number of HFLD1 conidia.By using this method,we demonstrated that both MpTLP2 and MpTLP3are capable to inhibit the growth of HFLD1 conidia.Thus,TLPs are of great importance in defense against HFLD1 infection in M.persicae. |
