Protein phosphorylation is a prerequisite for the Ca2+-dependent activation of Arabidopsis NADPH oxidases and may function as a trigger for the positive feedback regulation of Ca2+ and reactive oxygen species

►ROS production by AtRbohF is synergistically activated by Ca2+ and phosphorylation. ►Protein phosphorylation-induced activation of AtRbohF is independent of Ca2+. ►Protein phosphorylation is prerequisite for Ca2+-dependent activation. ►Phosphorylation of Rboh is the initial trigger for the plant Ca2+-ROS signalling network.