Abstract
Constitutive expression of Odorant-Binding Proteins (OBPs) in antennae and other body parts has been examined mainly to infer their involvement in insect olfaction, while their regulation in response to semiochemical stimuli has remained poorly known. Previous studies of semiochemical response were basically done using electrophysiology, which integrates the response of the set of OBPs present in an antenna or sensillum, without revealing the regulation of OBPs or which ones might be involved. In this study we used boll weevil as a model and mined its OBPs by RNA-Seq to study their simultaneous antennal expression by qPCR under controlled semiochemical stimuli with aggregation pheromone and plant volatiles. In the absence of a semiochemical stimulus, 23 of 24 OBPs were constitutively expressed in the antenna in both sexes. Semiochemicals changed systemically the expression of OBPs in both sexes. There were different patterns of up- and down-regulation in female antennae for each semiochemical stimulus, consistent with female chemical ecology. On the other hand, the only response in males was down-regulation of some OBPs. We suggest that these systemic changes in OBP expression might be related to enhancing detection of the semiochemical stimuli and/or priming the olfactory system to detect other environmental chemicals.
Highlights
Odorant-Binding Proteins (OBPs) play a key role in the first step of insect olfaction
Recent research has documented the constitutive expression of OBPs in insects [e.g.10,11], and for the vast majority of OBPs, constitutive expression levels are higher in antennae than in other body parts, leading most authors to conclude that the OBPs are involved in olfaction of semiochemicals
Does the presence of semiochemical affect the level of expression of OBPs? Does exposure to a semiochemical trigger systemic up-regulation and/or down-regulation of a set of OBPs? If there is systemic up- and/or down-regulation, does it enhance the detection of the semiochemical or does it prime the olfactory system to detect other environmental chemicals?
Summary
For each AgraOBP, the level of gene expression was analyzed by ANOVA, with Log10N0,ik = μ + si + + tk(i) + εik, where μ is the grand mean, si is the effect of sex i, tk(i) is treatment within s, and εik is the error These analyses were conducted using Proc GLM in SAS 9.453. Statistical comparisons of the number of OBPs responding to stimuli between females and males or pheromone and plant volatiles were done using contingency table analysis with a log-linear model and binomial error, and quantitative comparisons of up- and down-regulation were done with a two-sample t-test. The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request
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