A eukaryotic input circuit: computationally designed receptors, synthetic
eukaryotic signal transduction pathways, and a synthetic signal sensitive
promoter that allow highly specific transcriptional induction in response
to an externally provided ligand is disclosed. The input circuit is able
to specifically bind a targeted substance and transmit a signal to the
nucleus where transcription of a gene is activated. An output circuit
serves as a simple readout system of the substance detected by the input
circuit. The readout circuit exemplified here is a degreening circuit
which causes plants to turn white. Activation of the degreening circuit
can be detected by eye, or remotely with a variety of machines
(hand-held, aircraft or satellite based) and is also resettable. When
linked the input circuit if operably linked to the output circuit,
produces a functional plant detector.