Local Positive Feedback Regulation Determines Cell Shape in Root Hair Cells

Abstract

The specification and maintenance of growth sites are tightly regulated during cell morphogenesis in all organisms. ROOT HAIR DEFECTIVE 2 reduced nicotinamide adenine dinucleotide phosphate (RHD2 NADPH) oxidase–derived reactive oxygen species (ROS) stimulate a Ca 2+ influx into the cytoplasm that is required for root hair growth in Arabidopsis thaliana . We found that Ca 2+ , in turn, activated the RHD2 NADPH oxidase to produce ROS at the growing point in the root hair. Together, these components could establish a means of positive feedback regulation that maintains an active growth site in expanding root hair cells. Because the location and stability of growth sites predict the ultimate form of a plant cell, our findings demonstrate how a positive feedback mechanism involving RHD2, ROS, and Ca 2+ can determine cell shape.