An ancient alkalinization factor informs Arabidopsis root development

Summary The power of hydrogen (pH) regulates virtually all cellular activities. In both plants and animals, cell-to-cell variations in pH correlate with key developmental transitions1–5, yet the underlying regulators and associated functions remain elusive. Here, we report that members of the REMORIN (REM) protein family function as inhibitors of the H+-ATPases thereby promoting extracellular pH (pHe) alkalinization. This, in turn, regulates various cell surface processes, including steroid hormone signaling, and coordinates developmental transitions in the Arabidopsis thaliana root. Inhibition of H+-ATPases by REMs represents an evolutionary innovation that predates the origin of the root system itself. This study thus uncovers an ancient alkalinization mechanism co-opted by the root developmental program and infers that pHe patterning may have shaped morphogenesis evolution. Competing Interest Statement The authors have declared no competing interest.