Nicotinic acetylcholine receptor beta1 subunit from the brown planthopper, Nilaparvata lugens: A-to-I RNA editing and its possible roles in neonicotinoid sensitivity.

Nicotinic acetylcholine (ACh) receptors (nAChRs) are ligand-gated ion channels which mediate fast cholinergic synaptic transmission in insect and vertebrate nervous systems. The nAChR agonist-binding site is formed by loops A-C present in alpha subunits together with loops D-F present in either non-alpha subunits or homomer-forming alpha subunits. A new non-alpha subunit was cloned from Nilaparvata lugens, a major rice pest in many parts of Asia, showing very high amino acid identity to other insect beta1 subunits, and was denoted as N. lugens beta1 (Nlbeta1). Six A-to-I RNA editing sites were found in Nlbeta1 N-terminal domain, in which only one site was previously reported in Drosophila melanogaster Dbeta1 and the other five were newly identified. Among the six editing sites, four caused amino acid changes, in which the site 2 (E2) and site 5 (E5) caused an N to D change in loop D (N73D) and loop E (N133D) respectively. E2 frequency was high in Sus (susceptible) strain and E5 frequency was high in Res (resistant) strain. By expressing in Xenopus oocytes, N73D editing was found to reduce the agonist potency of both ACh and imidacloprid, and the influence on ACh was more significant than on imidacloprid. By contrast, N133D editing only affected imidacloprid potency. These results indicated, although E2 and E5 editings both caused an N to D change in important loops, their roles in neonicotinoid insensitivity might be different.