Chemosensory protein genes of batocera horsfieldi (hope): identification and expression pattern

Chemoreception is an essential feature for selection of host plants by insects. Chemosensory proteins (CSPs) are a group of small proteins (approximately 13 kDa) that are expressed widely in various insect sensory appendages. Batocera horsfieldi (Hope) is a major pest of Popolus and utilizes a variety of semiochemicals for its mating and oviposition. However, no CSP gene has been identified in B. horsfieldi. Here, to obtain the DNA sequences of B. horsfieldi CSPs, we used both bioinformatics and experimental approaches to analyse the antennal expressed sequence tags (ESTs). Among 649 EST clones, three unique CSP sequences (BhorCSP1, 2 and 3) were identified and characterized from B. horsfieldi (Hope) antennal cDNA libraries based on their four conserved cysteine residues, which have a characteristic spacing pattern. A phylogenetic tree of BhorCSPs and other insect CSPs showed that BhorCSP1 and BhorCSP2 are more similar to CSPs of Tribolium castaneum than BhorCSP3. BhorCSP3 is closely related to CSPs of the Dipteran, Culex quinquefasciatus. Using reverse transcription polymerase chain reaction (RT-PCR) and real-time Q-PCR strategies, we examined the expression patterns of these three putative CSP genes in different tissues, sexes and developmental stages. Our analysis shows that all three genes were expressed in all tissues examined, including the antennae, labial palps, maxillary palps, legs, abdomen and wings but not in the head. Real-time Q-PCR results revealed that these CSP genes were expressed throughout the life of the adults, and the transcription levels of these genes depended on the sex, age and mating status of adults.