Adaptation Of Host Alteration Of Myzus Persicae

The study on host adaptability of insect is an important basis for population differentiation,and a hot spot for field study of coevolution theory.Peach aphid?Myzus persicae?is a species of polyphagous phloem-sucking insect which is serious damage to a variety of plants.As a matter of fact,peach aphids can be differentiated on differing host plants into different biotypes.Study on the molecular interaction and adaptability mechanisms of these insect biotypes on host plants can better understand the population outbreak of polyphagous pests and provides a theoretical basis for pest control.In the current study,two biotypes of Myzus persicae from tobacco?Nicotiana tabacum L.?and cabbage?Brassica oleracea L.?were examined with tobacco as the host plants.We aim to determine the induced resistance of plants and the adaptation mechanism of aphids,and specifically quantify phytohormone-mediated plant resistance and secondary metabolites,the salivary effectors and intestinal detoxification enzymes of aphids.The main research results are as follows:?1?The electrical penetration graph?EPG?was used to analyze the feeding behaviors of peach aphid.The results showed that cabbage-biotype of peach aphid had more penetration and probing?in terms of potential drops numbers?and shorter duration of phloem ingestion?E2 wave?than the tobacco-biotype aphid when fed on tobacco.In contrast,there was no significant difference between two biotypes of peach aphids when fed on cabbage plants.The quantitative real-time PCR?qPCR?results showed that the infestation of cabbage-biotype of aphid enhanced the gene expression of WIPK,lipoxygenase?LOX2?,allene oxide cyclase?AOC?and the transcription factor MYC2.The infestation of tobacco-biotype of aphid increased the gene expression of LOX2 but reduced WIPK.These results therefore suggested that the differences in the feeding behavior of two aphid biotypes were closely related to the JA signaling pathway of tobacco plants.?2?By artificially applying saliva of two biotypes aphids on tobacco leaves,we determined the regulation effect of aphid saliva on plant defensive signaling.The saliva from cabbage-biotype of aphid increased the gene expression of WIPK,LOX2,AOC and MYC2which associated with JA signaling pathway.In contrast,the saliva from tobacco-biotype of aphid increased the gene expression of LOX2 but decreased the gene expression of MYC2.We further quantified the effectors in aphids'saliva of two aphid biotypes,found that the gene expression of MpC002,Mp10,Mp42,MIF and RPS2 in the saliva of tobacco-biotype was higher than cabbage-biotype aphid,while the expression of GroEL was lower.We then selected three aphid effectors including Mp10,Mp42 and GroEL,and tranfected into tobacco plants with agrobacterium infiltration.The JA signal pathway were impaired in Mp10,Mp42and GroEL transfection tobacco plants.We further examined the feeding behaviors of aphid to confirm the effect of salivary effector of aphids,the time the cabbage-biotype of aphid spent in phloem feeding was increased,but the probing numbers were reduced when exclusively fed on Mp42 over-expressed tobacco plants.Thus,tobacco-biotype aphids can surpress the JA-mediated resistance by secreting the saliva protein Mp42 into tobacco plants.?3?The transcriptome sequencing was used to analyze the gut of two biotype aphids.The results showed that cabbage-biotype of aphid up-regulated 338 genes but down-regulated761 genes relative to tobacco-biotype of aphid when fed on tabacco plants.Among all the genes subjected to KEGG pathway annotation and enrichment analysis,37 enriched pathways were significantly up-regulated including cathepsin B and Histone H₂B,and 54 pathways were significantly down-regulated in cabbage-biotype aphid including glutathione S transferase?GST?and UDP-glucuronosyl transferase.Aathepsin B and glutathione S transferase were detoxification metabolism related gene.Through analysis of significant difference degree and gene expressed level,we selected five genes.The qPCR was given to verified the result of transcriptome sequencing.It is found that the results of qPCR are consistent with the transcriptome sequencing results.Furthermore,we found that the relative expression was reduced when cabbage-biotype of aphid moved from cabbage to tobacco.This indicated that the glutathione S transferase was related to the differences in the feeding behavior of two aphid biotypes.?4?By using HPLC to quantify the content of alkaloids in the tobacco plants,we found that the infestation of tobacco-biotype of aphid increased the content of nicotine but reduced the levels of cotinine,while the infestation of cabbage-biotype of aphid had little effect on these alkaloids.We further determine the feeding behaviour of tobacco-biotype of aphid on wildtype?wt?and nicotine-deficient mutant tobacco?irPMT?.The results showed that the total duration of phloem-feeding was not significant for two tobacco genotyeps,but total duration of xylem-feeding?G wave?was increased when tobacco-biotype of aphid feeding on nicotine-deficient mutant.It was suggested that although the tobacco-biotype of aphids had different respone to alkaloids,but the content of nicotine in tobacco had little effect on aphid feeding.In conclusion,the tobacco-biotype and cabbage-biotype of peach aphids on tobacco plants exhibited different feeding behavior and efficiency.Tobacco-biotype of aphids can secrete more salivary effectors i.e.Mp42 to surpress the JA-mediated induced defenses of tobacco plant,which reduced the probing frequency and enhanced phloem feeding of aphids.Furthermore,they also enhanced the expression of glutathione S transferase,a detoxifying metabolism related gene in the intestine.By contrast,cabbage-biotype of aphids had lower salivary effectors which barely surpressed the JA-mediated induced defenses,leading to lower feeding efficiency,and the intestinal detoxification metabolism related gene expression of glutathione S transferase was also decreased.Further quantifying three most important secondary metabolites in tobacco plants including nicotine content found that nicotine content had little effect on feeding behavior and efficiency of two aphid biotypes.This thesis clarified the characteristics of the feeding behaviors of tobacco-biotype and cabbage-biotype of peach aphids on tobacco plants,and revealed that the surpression of plant resistance and improve gut detoxifying metabolism were important adaptive strategies in switching the hosts,which enriched the study case of plant-insect molecular interaction and coevolutionary theory.