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

Abstract

Root 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. Using confocal microscopy paired with redox biosensors and dyes, we demonstrated that treatments that elevate ethylene levels led to increased hydrogen peroxide 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 like ethylene-treated Col-0 seedlings. The caprice and werewolf transcription factor mutants have decreased and elevated ROS levels, which are correlated with levels of root hair initiation. 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 EIN3/EIL1 dependent transcriptional regulation. Together, these results indicate that 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) in trichoblast cells. Genetic and biochemical approaches identified ethylene-regulated ROS producing enzymes that drive root hair initiation.