Molecular Characterization of Two Pheromone Binding Proteins and Quantitative Analysis of their Expression in the Beet Armyworm, Spodoptera exigua Hübner

Pheromone binding proteins (PBP) play an important role in insect pheromone communication. However, the PBP for the beet armyworm, Spodoptera exigua Hubner (Lepidoptera: Noctuidae), an important agricultural pest worldwide, remains unaddressed. We report the cloning of two PBP genes, SexigPBP1 and SexigPBP2, from the antennal cDNA of S. exigua by reverse transcriptase-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends-PCR (RACE-PCR). The deduced PBP amino acid sequences are characteristic of the odorant binding protein (OBP) family, although the two PBPs are only 44% identical. From an analysis of the genomic DNA, two introns and a similar intron/extron structural pattern were identified in each of the two PBP genes. RT-PCR analysis revealed that the two PBP genes are only expressed in antennae. Real-time PCR further indicated that the expression of SexigPBP1 is much higher than that of SexigPBP2, regardless of sex. However, the female expression levels for SexigPBP1 and SexigPBP2 are about 39% and 73%, respectively, relative to male levels. Finally, phylogenetic analysis suggested that PBPs from the Noctuidae are divided into three distinct groups based on the primary sequences.