MOLECULAR CLONING, EXPRESSION PATTERN OF MULTIDRUG RESISTANCE ASSOCIATED PROTEIN 1 (MRP1, ABCC1) GENE, AND THE SYNERGISTIC EFFECTS OF VERAPAMIL ON TOXICITY OF TWO INSECTICIDES IN THE BIRD CHERRY-OAT APHID

The ATP-binding cassette (ABC) transporters are important transmembrane proteins encoded by a supergene family. The majority of ABC proteins are primary active transporters that bind and hydrolyze ATP to mediate the efflux of a diverse range of substrates across lipid membranes. In this study, we cloned and characterized a putative multidrug resistance associated protein 1 (MRP1) from Rhopalosiphum padi encoded by ABCC1. Structural analysis showed that this protein has structural features typical of the ABC transporter family. Phylogenetic analysis indicated that the amino acid sequence was highly similar that of the corresponding protein from Acyrthosiphon pisum. Real-time quantitative polymerase chain reaction (PCR) analysis showed that ABCC1 was expressed throughout all R. padi developmental stages, with the highest level of expression in the fourth larval instar. We also examined ABCC1 expression in four different tissue types and found that it was most highly expressed in the midgut. Exposing R. padi to imidacloprid and chlorpyrifos increased ABCC1 expression. Furthermore, ABCC1 expression was higher in the imidacloprid-resistant (IR) and chlorpyrifos-resistant (CR) strains than in an insecticide-susceptible strain (SS) of R. padi. Exposing R. padi to verapamil in combination with insecticides significantly increased the toxicity of the insecticides. The respective synergy factor of CR and IR R. padi strain was 1.33 and 1.26, which was lower than that (2.72 and 1.64, respectively) of the SS. Our results clarify the biological function of ABCC1 in R. padi, particularly its role in insecticide resistance, and suggest novel strategies for pest management that use ABC transporter inhibitors to increase the effectiveness of insecticides.

The β-N-acetylhexosaminidase gene family in the brown planthopper, Nilaparvata lugens

β-N-Acetylhexosaminidases (HEXs) are enzymes that can degrade the chitin oligosaccharides that are produced by the activity of chitinases on chitin in insects. Using bioinformatic methods based on genome and transcriptome databases, 11 β-N-acetylhexosaminidase genes (NlHexs) in Nilaparvata lugens were identified and characterized. Phylogenetic analysis revealed a six-grouped tree topology. The O-Linked N-acetylglucosaminidase (O-GlcNAcase) group includes NlHex11, which harbours a catalytic domain that differs from that of the other 10 NlHexs. Observations of the expression of NlHexs during different developmental stages revealed that NlHex4 is expressed with periodicity during moulting. Although the tissue-specific expression patterns of most NlHexs were nonspecific, NlHex4 was found to be expressed mainly in the female reproductive system as well as in the integument. RNA interference (RNAi) demonstrated failure to shed the old cuticle only in the nymphs treated with double-stranded RNA (dsRNA) targeting NlHex4, and these nymphs eventually died; no observable morphological abnormalities were found in insects treated with dsRNAs targeting the other 10 NlHexs. Based on this study and our previous analyses, a '5 + 1 + 3' pattern of chitinolytic enzymes is proposed, in which five chitinases, one NlHEX and three chitin deacetylases are required for moulting in N. lugens. A better understanding of chitin metabolism in the hemimetabolous insect, N. lugens, would be achieved by considering three chitinolytic enzyme families: chitinase, chitin deacetylase and β-N-acetylhexosaminidase.