Abstract: 【Objective】The objective of this study is to clarify the sequence properties and distribution of odorant binding protein (OBP) in the western flower thrips (Frankliniella occidentalis), which would be favorable for throwing light on the mechanism of insect olfaction perception and lay a basis for controlling the target pests by interfering with insect chemoreception.【Method】The OBP gene from F. occidentalis (FoccOBP1) was cloned using RT-PCR and RACE-PCR strategies. Nucleotide sequence was analyzed using DNAMAN software. Homology was analyzed using BLAST. A phylogenetic tree was constructed using neighbor-joining of MEGA 6.0. The secondary structure and three-dimensional model of FoccOBP1 were predicted using Chou & Fasman and SWISS MODEL, respectively. Expression profiles of FoccOBP1 at different developmental stages and in different tissues of the adults were assayed using real-time quantitative PCR. 【Result】 The OBP gene in F. occidentalis was cloned and named as FoccOBP1. The number in GenBank is KM527948. The full length of FoccOBP1 cDNA is 660 bp, contains a 450 bp open reading frame (ORF) encoding a putative protein of 149 amino acids with a molecular mass of 16.39 kD and an isoelectric point of 7.46. The non-coding district of 3′ and 5′ end is 172 bp and 38 bp, respectively, there is a polyA structure of eukaryotes. The deduced amino acid sequence possesses a putative signal peptide of 22 amino acid residues at the N terminus and contains the typical six-cysteine signature of insect OBPs. The arrangement of C1-X₂₆-C2-X₃-C3-X₄₀-C4-X₉-C5-X₈-C6 conform to six conservative cysteine site of the typical OBPs structural model. There are three lipotropism areas in amino acid sequence. A lipotropy pocket significantly was formed by 74-83 amino acid residues, which could be a fat-soluble binding site of odor molecules. Three OBPs of Hemiptera insects, 10 OBPs of Homoptera insects and FoccOBP1 amino acid sequence were clustered into one group by distance tree, and among them FoccOBP1 protein had high homolog with Apolygus lucorum AlucOBP8 (GenBank number is AFJ54049.1), Adelphocoris lineolatus AlinOBP5 (GenBank number is ACZ58031.1) and Lygus lineolaris LlinOBP2 (GenBank number is AHF71029.1) of Hemiptera insects, and Aphis gossypii AgosOBP7（GenBank number is AGE97637.1), Aphis glycines AglyOBP7 (GenBank number is AHJ80893.1), Rhopalosiphum padi RpadOBP7 (GenBank number is AHL30243.1) and so on of Homoptera insects, suggesting that these genes likely developed from a common ancestral gene. Secondary structure of FoccOBP1 predicted showed that FoccOBP1 had more α-helices, followed by beta-fold and less angle. The results of FoccOBP1 expression at different development stages revealed that this gene was highly expressed in nymph and 1-day-old adult. Expression levels reduced gradually with ages of adult and had differences with adult sex. The results of FoccOBP1 expression in different tissues revealed this gene was specifically expressed in the antennae. The reconstruction of expression plasmid pET-30a (+)/FoccOBP1 was constructed successfully. 【Conclusion】The sequence characteristics of nucleotides and amino acids of FoccOBP1 were clarified. The secondary structure and three-dimensional model of FoccOBP1 were analyzed. Temporal and spatial expression pattern of FoccOBP1 was clarified, indicating that FoccOBP1 may play an important role in olfactory reception, locating food sources, synthesis of pheromone and mating of F. occidentalis. The reconstruction of expression plasmid pET-30a (+)/ FoccOBP1 was constructed successfully, which is a basis of expression, purity and function of FoccOBP1 protein.

Key words: Frankliniella occidentalis, odorant binding protein (OBP), molecular cloning, sequence analysis, expression profile