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Abamectin treatment affects glutamate decarboxylase expression and induces higher GABA levels in the citrus red mite, Panonychus citri

Dou, Wei, Xia, Wen-Kai, Niu, Jin-Zhi, Wang, Jin-Jun
Experimental & applied acarology 2017 v.72 no.3 pp. 229-244
Citrus, Panonychus citri, abamectin, acaricide resistance, acarology, adults, gamma-aminobutyric acid, genes, glutamate decarboxylase, glutamic acid, high performance liquid chromatography, larvae, messenger RNA, mites, neurotransmitters, nucleotides, open reading frames, pests, quantitative polymerase chain reaction, reverse transcriptase polymerase chain reaction
The citrus red mite, Panonychus citri, is one of the most economically and globally destructive mite pests of citrus. Acaricide resistance has been a growing problem in controlling this pest. As the main inhibitory neurotransmitter in organisms, γ-aminobutyric acid (GABA) is synthesized from the amino acid glutamate by the action of glutamate decarboxylases (GADs). In the present study, one novel GAD gene, PcGAD, was identified and characterized from P. citri. The opening reading frame of PcGAD contained 1548 nucleotides that encode 515 amino acids. The subsequent spatiotemporal expression pattern by RT-qPCR revealed that the expression levels of PcGAD were significantly higher in larvae than in adults. Challenging with various concentrations of abamectin resulted in the upregulation of PcGAD transcript levels. Furthermore, biochemical characterization indicated that changes in GAD activity coincided with its mRNA levels. High-performance liquid chromatography confirmed that the GABA contents of P. citri increased upon abamectin treatment. The application of abamectin induces PcGAD expression and activates GAD activity, thereby resulting in an increase in GABA content in P. citri, which contributes to the adaptability of the mite to abamectin challenge.