Functional characterisation of Sirex noctilio chemosensation genes

Abstract

Insects rely on olfaction and gustation to interact with their surrounding environment. The highly sophisticated and complex chemosensory system behind smell and taste has received considerable attention due to its potential to contribute to the development of pest control strategies. This is because elucidating the molecular basis of chemosensation can be exploited in the design of behaviour-modifying chemical molecules. To gain a better understanding of the molecular basis of Sirex noctilio Fabricius (Hymenoptera: Siricidae) chemosensation we used RNA sequencing to create the most comprehensive comparison to date of chemosensation gene expression between olfactory and non-olfactory appendages of this representative of an ancient hymenopteran group. We compared gene expression between 15 transcriptome datasets to identify sex-, tissue-, and developmental stage-specific chemosensation genes. Sirex noctilio has 129 candidate chemosensation genes consisting of 45 olfactory receptors (OR), 12 gustatory receptors (GR), 48 ionotropic receptors (IR), 14 odourant binding proteins (OBP), 9 chemosensory proteins (CSP), and one sensory neuron membrane protein (SNMP). ORs and OBPS were enriched in olfactory appendages whereas GRs, IRs, CSPs, and the SNMP exhibited variable expression profiles across tissues. Developmental stage and tissue type, and to a lesser extent sex, influenced the expression of chemosensory genes. Several differentially expressed genes were identified. The antennae-, ovipositor- and leg-biased chemosensation genes identified are of particular interest due to the olfactory function, oviposition site-selection function and sexual dimorphism of these tissues, respectively. Based on expressed OR transcripts the chemoreceptive spectrum is largely similar between males and females. However, if relative expression levels of ORs correlate with sensitivity then females could have enhanced odour sensitivity. Sex- and tissue-specific genes are promising targets for future deorphanisation studies which could aid the identification of novel attractants or repellents for biorational pest management.