Ethylene signaling increases reactive oxygen species accumulation to drive root hair initiation in Arabidopsis

Abstract

ABSTRACTRoot hair initiation is a highly regulated aspect of root development. The plant hormone, ethylene, and its precursor, 1-amino-cyclopropane-1-carboxylic acid (ACC), induce formation and elongation of root hairs. We asked whether elevated ethylene induced root hair formation by increasing reactive oxygen species (ROS) synthesis in hair cells. Using confocal microscopy paired with redox biosensors and dyes, we demonstrated that treatments that elevate ethylene levels led to increased ROS accumulation in hair cells prior to root hair formation. In two ethylene-insensitive mutants, etr1-3 and ein3/eil1, there was no increase in root hair number or ROS accumulation. Conversely, etr1-7, a constitutive ethylene signaling receptor mutant, has increased root hair formation and ROS accumulation similar to ethylene-treated wild type seedlings. The rhd2-6 mutant, with a defect in the gene encoding a ROS synthesizing Respiratory Burst Oxidase Homolog C (RBOHC) and the prx44-2 mutant defective in a class III peroxidase, showed impaired ethylene-dependent ROS synthesis and root hair formation and decreased RBOH enzyme activity compared to Col-0. Together, these results support a model in which ethylene increases ROS accumulation through RBOHC and PRX44 to drive root hair formation.SUMMARY STATEMENTThe gaseous hormone ethylene increases root hair initiation by elevating reactive oxygen species (ROS) levels. Genetic and biochemical approaches identified ethylene-regulated ROS producing enzymes that drive root hair initiation.