Identification And Expression Profiling Of Odorant Binding Protein Genes In The Diamondback Moth, Plutella Xylostella (L.)

The olfactory system is essential for the survival and reproduction of insects. They rely on this system for the perception of odorants, hosts, predators and maintaining populations. Odorant binding proteins (OBPs) are able to bind various hydrophobic odorant molecules and transport them through the hemolymph to the dendrite membrane of the olfactory sensory neurons, which play an important role in the process of communication between the insect and its environment. The diamondback moth (DBM) is an important pest of cruciferous crops. To clarify its OBPs can help understand its olfactory mechanism thoroughly and lay the foundation for effective pest management. Based on the genome data and expression data of DBM, bioinformatics and qRT-PCR were applied to identify the OBPs and analyze their gene structure and expression pattern. The primary results are as follows:1. Based on the genome data of DBM,39 putative OBPs were identified. These OBPs are located on 20 different scaffolds, which included 11 OBPs being located on scaffold 174 and 4 OBPs on scaffold 44. There were 5 scaffolds with 2 OBPs respectively and 13 OBPs singly distributed on one scaffold.2. Sequence analysis of OBPs showed that the majority of OBPs consisted of 120-180 amino acids and contained 1-4 exons. Among these genes,6 pairs of OBPs showed a high similarity in sequence structure, including PxylOBP16 and PxylOBP20, PxylOBP17 and PxylOBP19, PxylOBP14 and PxylOBP24, PxylOBP29 and PxylOBP34, PxylOBP7 and PxylOBP8, PxylOBP26 and PxylOBP27.3. The phylogenetic analysis of six insects (Plutella xylostella, Bombyx mori, Manduca sexta, Helicoverpa armigera, Danaus plexippus, Heliothis virescens) suggested that PxylOBP37, PxylOBP38 and PxylOBP39 belonged to the PBPs sub-family. PxylOBP35 belonged to the GOBP1 sub-family, and PxylOBP36 to the GOBP2 sub-family. PxylOBP29, PxylOBP30, PxylOBP31, PxylOBP32, PxylOBP33 and PxylOBP34 were placed in the ABPs sub-family.4. Further gene expression analysis of DBM showed that the expression levels of OBPs in male adult, male head and female head were high but low in all other developmental stages or tissues. The expression pattern of DBM in different developmental stages and tissues using qRT-PCR technique indicated that the OBPs in virgin male were specific. The results also showed that the expression level of OBPs in male was higher than in female, no matter mated or virgin adults. The expression level of OBPs in mated female was higher than in virgins but the opposite in male. OBPs showed a higher expression level in antennae of males than in females. It is suggested that OBPs are more important for adults, especially for male adults than in larvae.5. In addition, the expression level of OBPs in DBM treated with host odor was detected and showed that the gene expression levels could be up regulated in first-, third- and fourth-instar larvae, as well as in both virgin and mated adults. The most significant up-regulation of OBPs was detected in virgin males, followed by first-, third-, and fourth-instar larvae. The results suggested that OBPs of DBM are crucial in host location.