Optogenetic Ca2+ signals in Arabidopsis roots suppress auxin responses and reversibly slow growth
Authors used the light-gated channel XXM2.0 to impose Ca2+ signals on Arabidopsis root cells and tested how calcium modulates the response to exogenous auxin.
A research team reported in Nature Communications that light-controlled calcium signals in Arabidopsis root cells reduce the response to exogenously applied auxin. The authors expressed XXM2.0, a Ca2+-permeable variant of Channelrhodopsin 2, to impose defined cytosolic Ca2+ signatures on living roots nature.com
Nature Communicationsnature.comOpen source ↗. According to the authors, repetitive light activation triggered cytosolic Ca2+ signals, which suppressed membrane depolarization and Ca2+ transients evoked by exogenous auxin.
Plants must balance growth with arrest, especially under stress, and auxin signaling is a central regulatory hub in this process. The mechanisms that tune auxin signaling in real time were unknown. Until now, plant Ca2+ signals have mostly been provoked by chemical probes or by changes in the composition of the extracellular solution. The authors note that these approaches are often invasive, prone to off-target effects, or inevitably alter the plasma membrane potential.
Light-gated channels in root cells
XXM2.0 and the light-gated anion channel GtACR1 were expressed under the UBQ10 promoter. Both were fused at the C-terminus to eYFP and combined with a retinal-generating dioxygenase. Confocal microscopy showed that both channels localized predominantly to the plasma membrane of root cells.
The team recorded membrane potential with sharp microelectrodes in the meristematic zone of 3–5-day-old seedlings. A 1-s blue light pulse (100 µE) electrically excited cells expressing either XXM2.0 or GtACR1. Trains of ten pulses at 30-s intervals produced repeated depolarizations, reproducible within the same cell and between different seedlings nature.com
Nature Communicationsnature.comOpen source ↗. Ca2+ signals in XXM2.0 seedlings were followed with the R-GECO1 sensor.
Auxin response and root growth
Prolonged optogenetic Ca2+ stimulation affected auxin-responsive transcriptional reprogramming. As a phenotypic output, the authors observed reversible inhibition of root growth through suppression of cell division and elongation.
The authors also identified a candidate CaM7–CNGC14 module that likely mediates Ca2+-dependent gating of responsiveness to exogenous auxin and Ca2+-dependent root growth inhibition. They describe the work as a synthetic biology approach to decompose calcium–auxin crosstalk in plant cells. In their conclusion, optogenetically imposed cytosolic Ca2+ signals act as dynamic regulators of auxin susceptibility in roots.
