Abstract: Polyphenol oxidase is the predominant enzyme in saliva of piercing-sucking insects. It can interfere with the normal oxidation-reduction reaction in host plants of insects and make food source more acceptable for itself. Insect laccase-1 (lac-1) belongs to the polyphenol oxidase family, and it has been verified that it is involved in the iron homeostasis, immune defense and detoxification. But the function of lac-1 in Bemisia tabaci is not clear. To determine the function of lac-1 gene in different tissues of Bemisia tabaci Middle East-Asia Minor 1 (MEAM1), lac-1 gene in B. tabaci MEAM1 was cloned using RACE method and named Btlac-1 (GenBank accession no. JQ966215). Btlac-1 contains an open reading frame (ORF) of 2 733 bp encoding 910 amino acids, and the encoded protein has three typical Cu-oxidase domains in polyphenol oxidase family, suggesting that Btlac-1 belongs to blue copper-containing polyphenol oxidase family. Homology analysis showed that Btlac-1 shares 58% amino acid sequence identity with lac-1 genes from Nephotettix cincticeps and Acyrthosiphon pisum. Gene transcript analysis revealed that lac-1 could be expressed at every developmental stage, and the highest expression level was observed at the adult stage, suggesting that lac-1 might play an important role during the adult stage. In addition, the transcriptional level of Btlac-1 in the midgut was higher than those in cephalothorax and abdomen tissues. These results provide clues to further understanding the physiological role of lac-1 in feeding in B. tabaci, and also a basis for exploring the interaction mechanism between piercing-sucking insects and plants.

Key words: Bemisia tabaci Middle East-Asia Minor 1, lac-1, polyphenol oxidase, expression profile, Real-time quantitative PCR