Distinct Subfamilies of Odorant Binding Proteins in Locust (Orthoptera, Acrididae): Molecular Evolution, Structural Variation, and Sensilla-Specific Expression

Abstract

Odorant binding proteins (OBPs) play an important role in insect olfaction, facilitating transportation of odorant molecules in the sensillum lymph. While most of the researches are concentrated on Lepidopteran and Dipteran species, our knowledge about Orthopteran species is still very limited. In this study, we have investigated OBPs of the desert locust Schistocerca gregaria, a representative Orthopteran species. We have identified 14 transcripts from a S. gregaria antennal transcriptome encoding SgreOBPs, and recapitulated the phylogenetic relationship of SgreOBPs together with OBPs from three other locust species. Two conserved subfamilies of classic OBPs have been identified, named I-A and II-A, exhibiting both common and subfamily-specific amino acid motifs. Distinct evolutionary features were observed for subfamily I-A and II-A OBPs. Surface topology and interior cavity were elucidated for OBP members from the two subfamilies. Antennal topographic expression revealed distinct sensilla- and cellular- specific expression patterns for SgreOBPs from subfamily I-A and II-A. These findings give first insight into the repertoire of locust OBPs with respect to their molecular and evolutionary features as well as their expression in the antenna, which may serve as an initial step to unravel specific roles of distinct OBP subfamilies in locust olfaction.

Expression of odorant‐binding proteins in mouthpart palps of the desert locust Schistocerca gregaria

“…The presence of Orco‐positive cells in the palps leads to the question of what types of OBPs may be expressed in sensilla of the palps. In a previous study we identified 14 antennal OBPs of desert locust S. gregaria (Jiang et al , ). Specific primers for each of the 14 OBPs were employed in RT‐PCR experiments to assess cDNA from maxillary and labial palps for OBP expression.…”

“… Overview of the expression of OBPs in either sensilla basiconica and/or sensilla chaetica of the antennae (Jiang et al , ; ) or palps of Schistocerca gregaria . The expression pattern was similar in labial and maxillary palps. …”

“…OBPs are supposed to be involved in solubilizing and transferring the hydrophobic odorants, but may have additional functions as well (Pelosi, ; Xu et al , ; Pelosi et al , ; ). Although most of our knowledge about OBPs is based on studies concentrating on holometabolous dipteran and lepidopteran species (Vogt et al , ; Robertson et al , ; Harada et al , ; Schultze et al , ; Pelosi et al , ), progress has also recently been made in analysing OBPs of hemimetabolous locusts, notably the desert locust S. gregaria and the migratory locust L. migratoria (Jin et al , ; Xu et al , ; Zhang et al , ; Wang et al , ; ; Zhang et al , ; Jiang et al , ; ; Pregitzer et al , ; Zhang et al , ; Li et al , ).…”

“…OBPs are small water‐soluble proteins of ~110–200 amino acids, which are supposed to solubilize the mostly lipophilic odorous compounds and may also be involved in signal transduction or termination (Vogt et al , ; Sandler et al , ; Tegoni et al , ; Große‐Wilde et al , ; ; Leal, ; Suh et al , ). Analysing the repertoire of potential OBPs of S. gregaria , we have identified 14 antennal OBPs from an antennal transcriptome (Jiang et al , ), which is a relatively small number compared with the large repertoire (119) of odorant receptors (ORs) (Pregitzer et al , ). In the closely related migratory locust Locusta migratoria , 16 OBPs have been identified, and 142 ORs were found in genome and antennal transcriptome analysis (Ban et al , ; Xu et al , ; Yu et al , ; Wang et al , ; ).…”

“…In the closely related migratory locust Locusta migratoria , 16 OBPs have been identified, and 142 ORs were found in genome and antennal transcriptome analysis (Ban et al , ; Xu et al , ; Yu et al , ; Wang et al , ; ). An evaluation of the topographic expression pattern for the OBP subtypes in the antennae revealed sensilla‐specific and cell‐specific co‐expression of distinct OBP subtypes in S. gregaria (Jiang et al , ; ).…”