Optogenetic Ca2+ signals tune auxin response in Arabidopsis

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 doi.org. According to the authors, repetitive light activation triggered cytosolic Ca2+ signals, which suppressed membrane depolarization and Ca2+ transients evoked by exogenous auxin doi.org.

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 doi.org.

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 doi.org.

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 doi.org. Ca2+ signals in XXM2.0 seedlings were followed with the R-GECO1 sensor doi.org.

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 doi.org.

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 doi.org. 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 doi.org.

Optogenetic Ca2+ signals in Arabidopsis roots suppress auxin responses and reversibly slow growth

Light-gated channels in root cells

Auxin response and root growth

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