Ca2+ signature gates early auxin signaling in Arabidopsis roots

preprint Ca2+ signature gates early auxin signaling in Arabidopsis roots draft Huifang Song author Angel Baudon author Matthias Freund author Marek Randuch author 6ac4636d-15b2-11ec-abd3-fb8df79972ae Aleš Pěnčík author Novák Ondřej author Zhaohui He author Kerstin Kaufmann author Nan Li author Matthew Gilliham author Jiří Friml author 4159519E-F248-11E8-B48F-1D18A9856A870000-0002-8302-7596 Rainer Hedrich author Shouguang Huang author JiFr department Cyclic nucleotides as second messengers in plants project Guanylate cyclase activity of TIR1/AFBs auxin receptors project 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 early auxin signalling 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 early auxin signalling. Our study thus introduces a synthetic biology approach 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. 2026 eng bioRxiv10.1101/2025.10.04.680446 https://research-explorer.ista.ac.at/record/23145 Song H, Baudon A, Freund M, et al. Ca2+ signature gates early auxin signaling in Arabidopsis roots. bioRxiv. doi:<a href="https://doi.org/10.1101/2025.10.04.680446">10.1101/2025.10.04.680446</a> H. Song, A. Baudon, M. Freund, M. Randuch, A. Pěnčík, N. Ondřej, Z. He, K. Kaufmann, N. Li, M. Gilliham, J. Friml, R. Hedrich, S. Huang, BioRxiv (n.d.). Song, Huifang, et al. “Ca2+ Signature Gates Early Auxin Signaling in Arabidopsis Roots.” BioRxiv, doi:<a href="https://doi.org/10.1101/2025.10.04.680446">10.1101/2025.10.04.680446</a>. H. Song et al., “Ca2+ signature gates early auxin signaling in Arabidopsis roots,” bioRxiv. . Song, H., Baudon, A., Freund, M., Randuch, M., Pěnčík, A., Ondřej, N., … Huang, S. (n.d.). Ca2+ signature gates early auxin signaling in Arabidopsis roots. bioRxiv. <a href="https://doi.org/10.1101/2025.10.04.680446">https://doi.org/10.1101/2025.10.04.680446</a> Song, Huifang, Angel Baudon, Matthias Freund, Marek Randuch, Aleš Pěnčík, Novák Ondřej, Zhaohui He, et al. “Ca2+ Signature Gates Early Auxin Signaling in Arabidopsis Roots.” BioRxiv, n.d. <a href="https://doi.org/10.1101/2025.10.04.680446">https://doi.org/10.1101/2025.10.04.680446</a>. Song H, Baudon A, Freund M, Randuch M, Pěnčík A, Ondřej N, He Z, Kaufmann K, Li N, Gilliham M, Friml J, Hedrich R, Huang S. Ca2+ signature gates early auxin signaling in Arabidopsis roots. bioRxiv, <a href="https://doi.org/10.1101/2025.10.04.680446">10.1101/2025.10.04.680446</a>. 231752026-10-19T11:51:47Z2026-10-22T09:15:44Z