Abstract
Olfactory plasticity, which is one of the major characteristics of density-dependent phase polyphenism, plays critical roles in the large-scale aggregation formation of Locusta migratoria. It is still unknown whether odorant-binding proteins (OBPs) are involved in phase-related olfactory plasticity of locusts, despite the confirmed involvement of several types of olfactory perception genes. In this study, we performed a large-scale search for OBPs and verified their expression patterns in the migratory locust. We identified 17 OBPs in the L. migratoria genome, of which 10 were novel, and we found their scattering distribution characteristics by mapping the genomic loci. Next, we revealed that these OBPs with close phylogenic relationships displayed similar tissue-specific expression profiles by a combined analysis of qRT-PCR and phylogenetic tree reconstruction. In all identified locust OBPs, seven OBPs showed differential mRNA expression levels in antenna tissue between gregarious and solitarious nymphs. Six of these seven OBPs displayed higher mRNA expression in the antennae of gregarious nymphs. The mRNA expression of LmigOBP2 and LmigOBP4 increased during gregarization and decreased during solitarization. RNAi experiments confirmed that only LmigOBP4 regulates the behavioral traits to affect gregarious behavior. These results demonstrated that OBPs also play important roles in the regulation of phase-related behavior of the locusts.
Highlights
The olfactory sense plays a critical role in behaviors related to food selection, host seeking, courtship, aggregation, and avoidance in insects when receiving external chemical cues (Leal, 2005; Pelosi et al, 2006; Benton, 2007)
Based on the L. migratoria genome assembly v.2.4, we have identified 17 genes encoding putative odorant-binding proteins (OBPs)
This study describes the identification, temporal-spatial expression, and effects on phase-related behavior of OBPs in the migratory locust
Summary
The olfactory sense plays a critical role in behaviors related to food selection, host seeking, courtship, aggregation, and avoidance in insects when receiving external chemical cues (Leal, 2005; Pelosi et al, 2006; Benton, 2007). OBPs belong to a large gene family with low protein conservation among family members (Vieira and Rozas, 2011). These genes are abundantly expressed in chemosensory sensilla, especially in the antennae and labial/maxillary palps. Depending on the types of ligands, OBPs transmit chemical signals to ORs to give rise to corresponding behavioral responses among conspecific insects and across species (Fan et al, 2011; Leal, 2013). OBPs can modulate feeding behavior by regulating the perception to host plant odorants or by affecting sucrose intake in response to bitter compounds (Swarup et al, 2014; Li et al, 2016)
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