Cloning and Functional Characterisation of the Duplicated RDL Subunits from the Pea Aphid, Acyrthosiphon pisum

Abstract

The insect GABA receptor, RDL (resistance to dieldrin), is a cys-loop ligand-gated ion channel (cysLGIC) that plays a central role in neuronal signaling, and is the target of several classes of insecticides. Many insects studied to date possess one <i>Rdl</i> gene; however, there is evidence of two <i>Rdls</i> in aphids. To characterise further this insecticide target from pests that cause millions of dollars' worth of crop damage each year, we identified the complete cysLGIC gene superfamily of the pea aphid, <i>Acyrthosiphon pisum</i>, using BLAST analysis. This confirmed the presence of two <i>Rdl</i>-like genes (RDL1 and RDL2) that likely arose from a recent gene duplication. When expressed individually in <i>Xenopus laevis</i> oocytes, both subunits formed functional ion channels gated by GABA. Alternative splicing of RDL1 influenced the potency of GABA, and the potency of fipronil was different on the RDL1_bd splice variant and RDL2. Imidacloprid and clothianidin showed no antagonistic activity on RDL1, whilst 100 μM thiacloprid reduced the GABA responses of RDL1 and RDL2 to 55% and 62%, respectively. It was concluded that gene duplication of <i>Rdl</i> may have conferred increased tolerance to natural insecticides, and played a role in the evolution of insect cysLGICs.