Defenses Mechanism Induced By Ostrinia Furnacalis (Lepidoptera: Crambidae) Feeding In Maize

Asian corn borer（ACB）,Ostrinia furnacalisn（Guenée）（Lepidoptera:Crambidae）is a major devastating insect pest in maize.The research on the ACB-induced resistance in maize will help to provide important ideas in IPM strategies for ACB control.In this study,we firstly evaluated the effects of ACB-induced resistance in maize on ACB performance,and then investigated the levels of gene expression and key metabolite in maize after ACB damage at different period of time.The study will help to reveal the defenses mechanism induced by ACB feeding in maize.Jingke 968 was chosen to evaluate the induced resistance level after ACB feeding for different period of time.The results of preference of consumption showed that the ACB consumptions of the leaves damaged for 8,12,24,48 and 72 h were significantly reduced than that of leaves in control（ACB feeding for 0 h）,with a decreased rate of 41%,48%,74%,60%and 61.5%,respectively.The result of a short-term feeding trial showed that efficiency of conversion of ingested food（ECI）,relative growth rate（RGR）and mean weight gain of ACB larvae which feeding on leaves damaged by ACB for 24 h were significantly lower than that of ACB feeding on leaves in control,but the relative consumption rate（RCR）and consumption index（CI）of of ACB larvae which feeding on leaves damaged by ACB for 24h became significantly higher.Life table study indicated that the developmental time for the egg to larva,the 1st to 2nd,the 5th instar larvae,pupal stage,the total pre-oviposition period（TPOP）and mean generation time（T）of individuals which feeding on leaves damaged by ACB for 24 h were significantly longer than that of ACB feeding on control leaves,but the finite rate of increase（λ）,intrinsic rate of increase（r）and net reproductive rate（R₀）of ACB which feeding on leaves damaged by ACB for 24 h became significantly lower.RNA-Seq was used to reveal the molecular mechanism of ACB-induced resistance in maize.The results showed that 4123（2645）,5121（3915）,5705（4488）and 5637（4396）of up（down）-regulated genes were observed after ACB feeding for 2,4,12 and 24 h,respectively.Genes differentially expressed were involved in benzoxazinoids biosynthesis,plant-pathogen interaction,plant hormone signal transduction,phenylalanine metabolism,terpenoid backbone biosynthesis and other metabolic pathway related to maize resistance to herbivores and disease.The significantly up-regulated genes included most of the terpene（TPS1,TPS2,TPS3,TPS6,TPS8,TPS10,TPS23 and TPS26）,JA（AOC,AOC4,AOS1,LOX1,LOX5,LOX9,LOX11,OPR1,OPR7 and OPR8）and benzoxazinoids biosynthesis-related genes（Bx1,Bx2,Bx3,Bx4,Bx5,Bx6,Bx7,Bx8,Bx9,Bx10,Bx11,Bx12,Bx13 and Bx14）.In addition,the genes of chloroplastic PPO1,wound induced protein 1、Bowman-Birk type wound-induced proteinase inhibitor,monoterpene synthase,terpene synthase 8,terpene synthase 2,（E）-beta-caryophyllene synthase,（E）-beta-farnesene synthase,lipoxygenase 5,peroxidase 12,1-aminocyclopropane-1-carboxylate oxidase,ACC oxidase and ethylene-responsive transcription factor,as well as Bx10,Bx11,Bx12,and Bx14 were all strongly and continuously expressed after ACB feeding for different period of time.The genes of trans-cinnamate 4-monooxygenase and AP2/EREBP transcription factor were strongly induced at early stage after ACB damage.The analysis of secondary metabolites was to further understand the metabolic reaction of maize toACB damage.The results indicated that the volatiles,benzoxazinoids,JA,JA-Ile and ABA showed dynamic responses to ACB feeding.The total emission of monoterpenoids and sesquiterpenes both reached the highest at ACB feeding for 48 h,respectively.The abundances of benzoxazinoids were also up-or down-regulated by ACB feeding except DHBOA-Glc,which was not induced by ACB feeding.The abundance of DHBOA,DIMBOA,DIBOA-Glc,TriBOA,DIBOA,DIMBOA-Glc and Cl-HMBOA-Glc reduced significantly after ACB feeding.The abundance of MBOA,HM2BOA-Glc,M2BOA,DIM2BOA-Glc,HDMBOA-Glc,HMBOA-Glc,DIM2BOA and HDM2BOA-Glc significantly increased after ACB feeding.In addition,we analyzed the levels of JA,JA-Ile,SA and ABA induced by ACB for 2,4,8 and 12 h.The levels of JA and JA-Ile were rapidly up-regulated by ACB feeding.The peak value of JA was observed at 2 and 4 h after ACB feeding,and the peak value of JA-Ile was observed at 2 h after ACB feeding.ABA content was up-regulated by ACB feeding at all induction time.SA level was not affected by ACB feeding.Y-tube olfactometer was used to test the behavior response of the ACB larval endoparasitoid,Macrocentrus cingulum（Brischke）,to maize odors emitted by ACB damage.The results showed that the M.cingulum females and males were both attracted by odors collected from the maize induced by ACB feeding for 4,12,24,48 and 72 h.In addition,the M.cingulum females and males were both attracted by Limonene,cis-3-hexen-1-ol,cis-3-hexenyl acetate,α-pinene,ocimene and farnesene.This study analyzed the gene expression and key metabolites of maize after ACB damage at different period of time,and identified the candidate genes and metabolites related to maize resistance to ACB.It is helpful to deepen the understanding of plant-herbivore interactions,and also provide rich gene resources for breeding resistance varieties of maize to ACB.