Expression of various odorant-response defective (odr) genes in the entomopathogenic nematode Heterorhabditis bacteriophora (Nematoda: Heterorhabditidae)

Abstract

Entomopathogenic nematodes (EPNs) exhibit complex host-seeking behaviour in soil and utilise the insect- and plant-derived odorants to locate and infect their insect hosts. The odorant response defective (odr) genes were identified in Caenorhabditis elegans through a forward genetic screen for worms defective in odour sensing. It is hypothesised that odr genes could be involved in insect host recognition by the EPNs, but no information is available on these genes or their functions in EPNs. Here, we investigated and characterised odr genes in the EPN Heterorhabditis bacteriophora. Seven orthologs of C. elegans odr genes were identified by in-silico analysis in H. bacteriophora, of which four genes (Hb-odr-2, Hb-odr-3, Hb-odr-4 and Hb-odr-10) could be amplified and cloned from the cDNA. The developmental stage-specific expression in infective juvenile (IJ), fourth stage juvenile (J4) and adult stage of H. bacteriophora showed that Hb-odr-2, Hb-odr-3 and Hb-odr-10 were up-regulated only at the IJ stage, whereas Hb-odr-10 was significantly up-regulated in all the developmental stages. Exposure to insect hemolymph resulted in high transcript accumulation of Hb-odr-3 but did not affect the expression of other Hb-odr genes. The in-situ hybridisation assays showed that Hb-odr-2 mRNA expression was localised at the region of the nerve ring while that of Hb-odr-3 in the region of pharyngointestinal valve and anterior esophagous of the IJs. Our results extend the knowledge of C. elegans odr genes to the entomopathogenic nematode H. bacteriophora. To the best of our information, this is the second investigation on the characterisation of odr genes in a parasitic nematode after the plant-parasitic species Meloidogyne incognita.