A Synthetic Light-Gated Gene Expression Switch for Plants

In the process of applying optogenetic sensors in plants to study phytohormone
patterning it has become clear that high-resolution sensing alone is not sufficient
- we also need to be able to perturb phytohormone patterning in high-resolution
to distinguish correlation from causation. Optogenetic actuators are minimally
invasive genetically encoded tools for modifying cell processes with maximal
spatiotemporal resolution, but a major challenge for designing optogenetic
actuators for plants is that they need to exhibit one target gene expression
state during plant growth in normal light-dark cycles, and an altered target gene
expression state following treatment with light spectra that are not found in a
horticultural environment. We have created an orthogonal synthetic light-gated
gene expression system for plants, by repurposing the cyanobacterial
CcaS-CcaR system, a photoreversible two-component signal transduction
systems, by semi-rational engineering. When tested by transiently transfecting
N. benthamiana, our system was inactive under blue light conditions and active
in the dark and under green, red and white light conditions. Furthermore, the
systems activity could be tuned by modulating the red-to-blue ratio of white
light. We are presently engineering the system for function in stably transformed
Arabidopsis plants and towards being inactive in ambient white
light and in the dark, be activated by green light and inactivated by blue or red
light. With these properties, the system will enable us to manipulate biological
processes with high-spatiotemporal resolution in a minimally invasive manner.