Characterization of glucose-induced glucose oxidase gene and protein expression in Helicoverpa armigera larvae

Caterpillar labial salivary enzyme glucose oxidase (GOX) plays an important role in plant-insect interactions by suppressing the caterpillar-induced nicotine production in tobacco plants. In the present study, we cloned and characterized the GOX gene (HaGox) from labial salivary glands of Helicoverpa armigera larvae using 3' and 5' RACE, homologous analysis, phylogenetic analysis, LC-MS/MS, and qRT-PCR. The deduced GOX amino acid sequence (606 amino acids) shares 99% and 76% identity with H. zea and Spodoptera exigua GOX, respectively, and is consistent with the GOX protein sequence identified from H. armigera labial salivary gland. These results confirmed that the HaGox encode the GOX protein. Transcript levels of HaGox in larval labial salivary glands were significantly higher than those in midgut and hemolymph, respectively, and those of caterpillars reared on tobacco leaves coated with 0.1%, 1%, and 10% glucose solutions were significantly higher than those reared on 0.01% glucose-coated leaves or control tobacco leaves. Western blot and native PAGE showed that GOX protein expression levels and GOX enzymatic activities also increased with dietary glucose. These results proved that GOX expressions in larval labial salivary glands induced by dietary glucose were exhibited not only on transcriptional levels, but also on translational/posttranslational levels.