Cell expansion is a central process in plant morphogenesis, and the elongation of roots and root hairs is essential for uptake of minerals and water from the soil. Ca2+ influx from the extracellular store is required for (and sets the rates of) cell elongation in roots1. Arabidopsis thaliana rhd2 mutants are defective in Ca2+ uptake and consequently cell expansion is compromised—rhd2 mutants have short root hairs2,3 and stunted roots. To determine the regulation of Ca2+ acquisition in growing root cells we show here that RHD2 is an NADPH oxidase, a protein that transfers electrons from NADPH to an electron acceptor leading to the formation of reactive oxygen species (ROS). We show that ROS accumulate in growing wild-type (WT) root hairs but their levels are markedly decreased in rhd2 mutants. Blocking the activity of the NADPH oxidase with diphenylene iodonium (DPI) inhibits ROS formation and phenocopies Rhd2-. Treatment of rhd2 roots with ROS partly suppresses the mutant phenotype and stimulates the activity of plasma membrane hyperpolarization-activated Ca2+ channels, the predominant root Ca2+ acquisition system. This indicates that NADPH oxidases control development by making ROS that regulate plant cell expansion through the activation of Ca2+ channels.
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We thank D. Graham and A. Dark for help with screening and cultivation, respectively; E. Ryan, P. Shaw and K. Roberts for comments on the manuscript; and P. Doerner for support. This work was funded by the BBSRC, the Gatsby Foundation, the Leverhulme Trust and the European Union.
The authors declare that they have no competing financial interests.
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Foreman, J., Demidchik, V., Bothwell, J. et al. Reactive oxygen species produced by NADPH oxidase regulate plant cell growth. Nature 422, 442–446 (2003). https://doi.org/10.1038/nature01485
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