Effects Of Volatiles From Lipaphis Erysimi-infested Arabidopsis On Lecanicillium Lecanii

Entomopathogenic fungi(EPFs)have been ignored as a research topic on plant-herbivore-natural enemy tritrophic interactions,due to their host searching inability.It is known that herbivore-induced plant volatiles(HIPVs)are the chemical cue for insect enemies;however,what is the effect of HIPVs on EPFs is still unknown.The objectives of this study were to(1)investigated the effect of Lipaphis erysimi induced Arabidopsis thaliana volatiles on the Lecanicillium lecanii;(2)analyze the active compounds in HIPVs;(3)assess the effect of active compounds in HIPVs on the toxicity related enzymes;(4)examine the effect of active compounds in HIPVs on the expression of appressorial formation related genes.The major results are showed below.1.Arabidopsis HIPVs induced by different densities of aphids were analyzed with GC-MS.Results showed that benzaldehyde,phenylacetaldehyde,decan-3-ol,methyl salicylate,menthol,methyl jasmonate,d-limonene,1-octen-3-ol,(E)-2-hexenal,(E)-2-nonenal,n-nonanal,(Z)-3-hexenol,n-hexyl acetate,n-nonanol and terpineols were the major compounds of aa-HIPVs.We found that HIPVs promoted conidial germination and appressorial formation rate,and improve the toxicity of L.lecanii against aphids.Five active compounds(menthol,methyl salicylic,benzaldehyde,phenylacetaldehyde and decan-3-ol)in 15 major compound in aphids-induced Arabidopsis volatiles(aa-HIPVs)were detected with Pearson-correlation analysis.The experiment demonstrated that conidial performance and toxicity of EPFs were induced by HIPVs.2.Synthetic compounds of menthol,methyl salicylic,benzaldehyde,phenylacetaldehyde and decan-3-ol were used to repeat bioassays.Among these five chemicals,menthol and methyl salicylic induced,while benzaldehyde,phenylacetaldehyde and decan-3-ol inhibited germination rate,appressorial formation and toxicity of L.lecanii.3 In the research of revealing biochemical mechanism,we detected the effects of active compounds on the activities of infection-related enzymes,extracellular protease and chitinase.Menthol,methyl salicylate and methyl jasmonate increased,while terpineol inhibited activities of extracellular protease.For chitinase,we did not find the related active chemical from filtered compounds.4 In EPFs,cAMP and PKA,MAPK and PMK1,CaM and CaMK gene were the key genes in cAMP,MAPK and Ca2+ signal pathway,respectively.The influence of active compounds in aa-HIPVs(menthol and methyl salicylate)on the expression of these genes in the conidia were tested with RT-PCR.The expression level of CaM and CaMK genes were induced by methyl salicylate,and cAMP and PKA genes were induced by menthol.In this study,our results showed that conidial performance and toxicity of EPFs were induced by HIPVs,and methyl salicylate and menthol were the key chemicals involved in this regulation.These two chemicals not only increased the extracellular protease activity,but also induced the Ca2+ and cAMP signal pathways to improve the conidial performance of EPFs.Accordingly,we believe that HIPVs are the chemical signals that connect plants and EPFs,and developed new and easier way for increasing conidial production and improving the pathogenicity of EPFs.