A green light-excitable FRET system for monitoring intracellular calcium levels in plant cells.

CFP/YFP-paired FRET is routinely used to estimate intracellular Ca2+ concentrations in vivo. This system, however, is excited with blue light, which is likely to invoke unexpected responses in plant cells. This report describes a new green light-excitable FRET system with an mKO2/mCherry pair. Plant cells expressing this newly constructed FRET system demonstrated its ability to monitor changes in cytosolic free calcium concentration. The new system is likely to find applications in studies of plant cells where undesirable blue light responses must be avoided.