Antioxidant Enzymatic Activities And C-Lectin Gene Responding Function Of Bactrocera Dorsalis Infected By Beauveria Bassiana (Bb07)

Bactrocera dorsalis（Hendel）(Diptera;Tephritidae is a dangerous pest with important economic significance,which has become a great threat to the development of fruit and vegetable industry.Currently,chemical and physical control measures are mainly used to control this pest in the field.However,due to its wide range of hosts and the rapid development of resistance,the difficulty of control is gradually increasing,and there is an urgent need to find an environmentally friendly and green control method.This thesis explores the effect of the pathogenic entomopathogenic fungus Beauveria bassiana（Bb07）on the reproductive ability and antioxidant enzyme system of B.dorsalis.In addition,some key C-type lectin（C-lectin）genes of B.dorsalis were studied to clarify their important roles in defensing B.bassiana infection,including Bd C-lectin S4,Bd C-lectin S12,and Bd C-lectin S31.Comparative transcriptomics technology was used to analyze the immune response mechanisms at different time points under the infection of Bb07.The results of this study will provide new ideas and data for the biological control and discovery of control targets for B.dorsalis,and they will also provide a theoretical basis for a deeper understanding of the interaction mechanism between B.dorsalis and pathogenic fungi.The main research results of this thesis are listed as follows:1.The effect of Bb07 infection on the egg laying amount and antioxidant enzyme activities in B.dorsalisThe effective lethal spore concentration range of Bb07 is 1×10⁷ to 1×10⁹spores/m L,with a lethal effect time of 4 days or more.The LC₅₀ of Bb07 infection on the 5th,6th,7th,and 8th days after treatment was 4.34×10⁸,1.92×10⁸,1.33×10⁸,and 1.19×10⁸ spores/m L,respectively.The oviposition of B.dorsalis after Bb07 LC₂₀ infection showed a trend of first increasing and then decreasing when compared with the control group,but an overall remarkerble reduction was detected with an extent of35.92%.On the first day after Bb07 infection,CAT,GSTs,MDA,and T-AOC in B.dorsalis were significantly lower than the normal level,indicating that the protective enzyme system in B.dorsalis was suppressed.The activities of SOD and POD were increased and played an important role in the2nd to 5th days after infection,thus restoring the T-AOC to the normal level and maintaining the balance of reactive oxygen species in B.dorsalis.2.Identification and analysis of the Bd C-lectin genes in B.dorsalis and functional studies of their response to Bb07 infectionBased on genomic and transcriptomic data of B.dorsalis,48 Bd C-lectin genes were identified,including 42 in the C-lectin-S subfamily and 6 in the C-lectin-X subfamily.Phylogenetic analysis and chromosomal localization indicated that the Bd C-lectin genes underwent species-specific expansion during evolution.The temporal and spatial expression patterns of Bd C-lectin genes showed that the expression levels were generally low expressed during different developmental stages of B.dorsalis,but differentially expressed in various adult tissues.Specifically,Bd C-lectin S4,S10,S34,and S36were highly expressed in the hemolymph;Bd C-lectin S12 and S23 were highly expressed in the fat body;and Bd C-lectin S3,S21,and S41 were highly expressed in the midgut.In response to low-dose Bb07 infection,Bd C-lectin S4,S12,S31,S36,and S38 were significantly upregulated.Interference with the expression of Bd C-lectin S4,S12,and S31 genes resulted in a significant decrease in the survival rate of B.dorsalis infected with Bb07,indicating that these Bd C-lectin genes play an important role in the defense against Bb07 infection.3.Transcriptomic analysis of B.dorsalis in response to Bb07 infectionBased on transcriptome sequencing data of B.dorsalis,differential gene expression was analyzed at three time points（36 h,48 h,and 96 h）after Bb07 infection,compared to the control treatment with0.05%Tween 80 for 36 h.A total of 3,812 differentially expressed genes were identified,with 236,528,and 3,048 genes differentially expressed at each time point,respectively.The increasing number of differentially expressed genes over time indicated a stronger resistance response of B.dorsalis to Bb07 infection in a time-courses.NR annotation and KEGG enrichment analysis of differentially expressed genes showed that most upregulated genes were immune-related at 36 h post-infection,and Toll pathway genes were significantly upregulated including various steps of immune progress,e.g.,pattern recognition,signal transduction,and effector release.These results indicated that those genes may play important roles in defense against Bb07 infection.At 48 h and 96 h post-infection,most differentially expressed genes were enriched in energy supply and protein synthesis pathways,suggesting that energy supply and material reserves are important factors for the successful defense against Bb07 infection in the late stage.