Abstract: Odorant binding proteins (OBPs) play important roles in the perception of host plant volatiles, but Minus-C OBPs (with only four conserved cysteins) and their functions are rarely addressed. In this study, a full-length cDNA of a Minus-C OBP gene from the rice striped stem borer, Chilo suppressalis (Walker), was cloned and identified by transcriptome analysis and RACE technology, which was named CsupOBP1 (GenBank accession no. KC492498). The sequence of CsupOBP1 contains a 423 bp open reading frame that encodes 141 amino acids, including a signal peptide of 18 amino acids at the N terminus and the four conserved cysteins of Minus-C OBPs. The results of real-time quantitative PCR (qRT-PCR) showed that CsupOBP1 was highly expressed in the larval heads, adult legs and wings of both sexes, and adult antennae of males. The expression level in female antennae was significantly lower than that in male antennae. Affinities of recombinant CsupOBP1 with 38 ligands were tested by fluorescence competitive binding assay. Beta-ionone showed the highest affinity (Ki=9.53 μmol/L) to CsupOBP1. In the electroantennogram (EAG) recording assay, beta-ionone elicited stronger EAG responses than other tested volatiles, and stronger response in males than in females, consistent with the results of binding assay and male antennae biased expression of CsupOBP1. Considering that beta-ionone is a common fragrant volatile of many host plants of C. suppressalis, we propose that CsupOBP1 functions to bind and transport beta-ionone and thus plays a role in finding host plants in C. suppressalis.

Key words: Chilo suppressalis, odorant binding protein, electroantennogram, tissue expression pattern, beta-ionone, fluorescence competitive binding assay