Molecular Characterization and Transcriptional Expression Analysis of ABC Transporter H Subfamily Genes in the Oriental Fruit Fly

Characterization and transcriptional expression of ABCG genes in Bactrocera dorsalis: Insights into their roles in fecundity and insecticidal stress response

The ATP-binding cassette (ABC) transporters are essential for regulating various physiological processes and insecticide resistance across different living organisms. ABCG subfamily genes have diverse functions in insects, but little is known about the function of ABCGs in a serious agricultural pest, Bactrocera dorsalis. In this study, 15 BdABCG genes were identified, and BdABCG6 and BdABCG11 were highly expressed in the pupal and adult stages, especially during the transition period from pupae to adults. Silencing of these two genes resulted in a significant reduction of egg production in B. dorsalis, confirming their importance in reproduction. Analysis of tissue expression patterns showed that most genes, including BdABCG1, 3, 8, and 14, exhibited tissue-specificity, with significantly higher expression levels observed in the intestine, Malpighian tubule, and fat body compared to other tissues. Meanwhile, the induction of malathion and avermectin can significantly upregulate the expression of the above four genes. Furthermore, knockdown of BdABCG3 by RNAi significantly increased the mortality of B. dorsalis upon exposure to avermectin, which suggested that BdABCG3 is involved in the transport or metabolism of avermectin in B. dorsalis. Overall, our work provides valuable insights into the function of BdABCGs involved in the reproduction and detoxification system of B. dorsalis.

Overexpression of ABCB transporter genes confer multiple insecticide tolerances in Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

Bactrocera dorsalis is a notable invasive pest that has developed resistance to several commonly used insecticides in the field, such as avermectin, beta-cypermethrin and malathion. Investigating the mechanisms of insecticide resistance in this pest is of paramount importance for ensuring its effective control. The ATP-binding cassette transporter subfamily B (ABCB) genes, responsible for encoding transmembrane efflux transporters, represent a potential source of insecticide detoxification activity or transportation that remains largely unexplored in B. dorsalis. In this study, seven BdABCB genes were identified and comprehensive analyzed based on the latest genome and transcriptome dataset. Subsequently, we characterized the expression profiles of these genes across different development stages and tissues, as well as under different insecticide exposures. The results showed that the BdABCB genes were expressed at all stages in B. dorsalis, with BdABCB2 and BdABCB7 being highly expressed in the pupal stage, while BdABCB5 and BdABCB6 were highly expressed in the larval stage. Besides, the BdABCBs were highly expressed in the detoxification metabolic tissues. Among them, BdABCB5 and BdABCB6 were significantly overexpressed in the midgut and Malpighian tubules, respectively. Furthermore, with the exception of BdABCB6, the expression levels of the other six BdABCBs were significantly up-regulated following induction with avermectin, beta-cypermethrin and malathion. Six BdABCBs (BdABCB1-5 and BdABCB7) were knocked down by RNA interference, and the interference efficiencies were 46.58%, 39.50%, 45.60%, 33.74%, 66.37% and 63.83%, respectively. After injecting dsBdABCBs, the mortality of flies increased by 25.23% to 39.67% compared to the control upon exposure to the three insecticides. These results suggested that BdABCBs play crucial roles in the detoxification or tolerance of B. dorsalis to multiple insecticides.

High-Sucrose Diet Exposure on Larvae Contributes to Adult Fecundity and Insecticide Tolerance in the Oriental Fruit Fly, Bactrocera dorsalis (Hendel)

Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) is one of the broad host ranges and economically-important insect pests in tropical and subtropical areas. A wide range of hosts means they have strong adaptation ability to changes in dietary macronutrients (e.g., sucrose and protein). However, the effects of dietary conditions on the phenotypes and genotypes of B. dorsalis are still unclear. In this study, we aimed to investigate the effects of larval dietary sucrose on the life history traits and stress tolerance of B. dorsalis, and its defense response at the molecular level. The results showed that low-sucrose (LS) induced decreased body size, shortened developmental duration, and enhanced sensitivity to beta-cypermethrin. Otherwise, high-sucrose (HS) diet increased developmental duration, adult fecundity, and tolerance to malathion. Based on transcriptome data, 258 and 904 differentially expressed genes (DEGs) were identified in the NS (control) versus LS groups, and NS versus HS groups, respectively. These yielded DEGs were relevant to multiple specific metabolisms, hormone synthesis and signaling, and immune-related pathways. Our study will provide biological and molecular perspective to understand phenotypic adjustments to diets and the strong host adaptability in oriental fruit flies.

Chromosome-level genome assembly reveals potential epigenetic mechanisms of the thermal tolerance in the oriental fruit fly, Bactrocera dorsalis

The oriental fruit fly, Bactrocera dorsalis (Hendel), has very strong ecological adaptability and phenotypic plasticity. Here, the genome of B. dorsalis was assembled into 549.45 Mb sequences with a contig N50 length of 12.81 Mb. Among, 95.67 % assembled genome sequences were anchored on six chromosomes with an N50 length of 94.63 Mb. According to the basic characteristics of the sex chromosomes of Tephritidae, the X chromosome of B. dorsalis was identified. Significant gene expansions were detected in several important gene families related to adaptability. In particular, we annotated 50 histone modification enzymes (HMEs) in this genome. A comparative transcriptome analysis indicated that 12 HME genes were differentially expressed in two thermo-tolerant strains (heat and cold). Interestingly, four and seven of the 12 HME genes responded to heat shock or cold hardening, respectively. These evidences suggested that the histone modification as an epigenetic modification may be involved in the thermal tolerance of B. dorsalis, but with different regulation mechanisms in thermal acclimation and hardening. The high quality genome of B. dorsalis provides an invaluable resource for further functional genomic study. Moreover, comparative genomic analysis will shed insights on revealing the mechanisms of adaptive evolution in this fly.

A Novel Reference for Bt-Resistance Mechanism in Plutella xylostella Based on Analysis of the Midgut Transcriptomes

Simple Summary

Plutella xylostella is a very serious pest to cruciferous vegetables. At present, the control methods used are mainly traditional insecticides and the cultivation of Bt crops. However, with the long-term and large-scale use of insecticides, the diamondback moth has developed strong resistance to many kinds of insecticides and Bt crops. The Cry1S1000 strain of P. xylostella used here is a strain with more than 8000 times resistance to Bt Cry1Ac protoxin. In this paper, we used transcriptome sequencing to determine the midgut transcriptome of the G88-susceptible strain, Cry1S1000-resistant strain and its corresponding toxin-induced strains to find more genes related to Bt resistance. Our results will provide a reference for optimizing the control strategy of diamondback moth resistance and improving the control efficiency of biopesticides and Bt crops.

Abstract

The diamondback moth, Plutella xylostella, is a lepidopteran insect that mainly harms cruciferous vegetables, with strong resistance to a variety of agrochemicals, including Bacillus thuringiensis (Bt) toxins. This study intended to screen genes associated with Bt resistance in P. xylostella by comparing the midgut transcriptome of Cry1Ac-susceptible and -resistant strains together with two toxin-treated strains 24 h before sampling. A total of 12 samples were analyzed by BGISEQ-500, and each sample obtained an average of 6.35 Gb data. Additionally, 3284 differentially expressed genes (DEGs) were identified in susceptible and resistant strains. Among them, five DEGs for cadherin, 14 for aminopeptidase, zero for alkaline phosphatase, 14 for ATP binding cassette transport, and five heat shock proteins were potentially involved in resistance to Cry1Ac in P. xylostella. Furthermore, DEGs associated with “binding”, “catalytic activity”, “cellular process”, “metabolic process”, and “cellular anatomical entity” were more likely to be responsible for resistance to Bt toxin. Thus, together with other omics data, our results will offer prospective genes for the development of Bt resistance, thereby providing a brand new reference for revealing the resistance mechanism to Bt of P. xylostella.