Ca2+ signature-dependent control of auxin sensitivity in Arabidopsis

Abstract Plants must continually balance growth with arrest, especially under stress. Auxin signaling acts as a central regulatory hub in this process, yet the mechanisms that dynamically tune auxin sensitivity in real time remain unknown. Here, we used the light-gated, Ca2+-permeable ChannelRhodopsin 2 variant XXM2.0 to optogenetically impose defined Ca2+ signatures on Arabidopsis root cells. Repetitive light activation triggered cytosolic Ca2+ signals that in turn suppressed auxin-induced membrane depolarization and Ca2+ transients. Moreover, prolonged optogenetic Ca2+ stimulation affects auxin-responsive transcriptional reprogramming. As phenotypic output, reversible inhibition of root growth by suppressing cell division and elongation was observed. We further identify a candidate CaM7–CNGC14 module that likely mediates Ca2+-dependent gating of auxin sensitivity. Our study thus introduces a new tool to decompose calcium– auxin crosstalk in plant cells, and demonstrates that optogenetically imposed cytosolic Ca2+ signals act as dynamic regulators of auxin susceptibility in roots. Competing Interest Statement The authors have declared no competing interest. Footnotes Strengthened the mechanistic aspect of the study by adding new genetic and physiological analyses supporting a candidate CaM7-CNGC14 module involved in Ca2+-dependent attenuation of auxin sensitivity.