A Minimal Cysteine Motif Required To Activate The SKOR K+ Channel Of Arabidopsis By The Reactive Oxygen Species H2O2

Abstract

Reactive oxygen species (ROS) are essential for development and stress signalling in plants. They contribute to plant defense against pathogens, regulate stomatal transpiration and influence nutrient uptake and partitioning. Although both Ca2+ and K+ channels of plants are known to be affected, virtually nothing is known of the targets for ROS at a molecular level. Here we report that a single cysteine (Cys) residue within the Kv-like SKOR K+ channel of Arabidopsis thaliana is essential for channel sensitivity to the ROS H2O2. We show that H2O2 rapidly enhanced current amplitude and activation kinetics of heterologouslyexpressed SKOR, and the effects were reversed by the reducing agent dithiothreitol (DTT). Both H2O2 and DTT were active at the outer face of the membrane and current enhancement was strongly dependent on membrane depolarization, consistent with a H2O2-sensitive site on the SKOR protein which is exposed to the outside when the channel is in the open conformation. Cys substitutions identified a single residue, C168 located within the S3 α-helix of the voltage sensor complex, to be essential for sensitivity to H2O2. The same Cys residue was a primary determinant for current block by covalent Cys S-methioylation with aqueous methanethiosulfonates. These, and additional data identify C168 as a critical target for H2O2, and implicate ROSmediated control of the K+ channel in regulating mineral nutrient partitioning within the plant.