Plants That Earn Their Keep

Could airport security gardens be the wave of the future? (“Please have photo ID and boarding pass ready and walk past the rhododenrons.”) How about a defensive line of bomb-sniffing tulips in Central Park in New York, or at the local shopping mall’s indoor waterfall, or lining the streets of Baghdad? Researchers at Colorado State University said Wednesday that they had created the platform for just such a plant-kingdom early warning system: plants that subtly change color when exposed to minute amounts of TNT in the air. They are redesigned to drain off chlorophyll — the stuff that makes them green — from leaves, blanching to white when bomb materials are detected. – New York Times: Plants That Earn Their Keep

Antunes MS, Morey KJ, Smith JJ, Albrecht KD, Bowen TA, et al. 2011 Programmable Ligand Detection System in Plants through a Synthetic Signal Transduction Pathway. PLoS ONE 6(1): e16292. doi:10.1371/journal.pone.0016292
Abstract: Background: There is an unmet need to monitor human and natural environments for substances that are intentionally or unintentionally introduced. A long-sought goal is to adapt plants to sense and respond to specific substances for use as environmental monitors. Computationally re-designed periplasmic binding proteins (PBPs) provide a means to design highly sensitive and specific ligand sensing capabilities in receptors. Input from these proteins can be linked to gene expression through histidine kinase (HK) mediated signaling. Components of HK signaling systems are evolutionarily conserved between bacteria and plants. We previously reported that in response to cytokinin-mediated HK activation in plants, the bacterial response regulator PhoB translocates to the nucleus and activates transcription. Also, we previously described a plant visual response system, the de-greening circuit, a threshold sensitive reporter system that produces a visual response which is remotely detectable and quantifiable.
Methodology/Principal Findings: We describe assembly and function of a complete synthetic signal transduction pathway in plants that links input from computationally re-designed PBPs to a visual response. To sense extracellular ligands, we targeted the computational re-designed PBPs to the apoplast. PBPs bind the ligand and develop affinity for the extracellular domain of a chemotactic protein, Trg. We experimentally developed Trg fusions proteins, which bind the ligand-PBP complex, and activate intracellular PhoR, the HK cognate of PhoB. We then adapted Trg-PhoR fusions for function in plants showing that in the presence of an external ligand PhoB translocates to the nucleus and activates transcription. We linked this input to the de-greening circuit creating a detector plant.
Conclusions/Significance: Our system is modular and PBPs can theoretically be designed to bind most small molecules. Hence our system, with improvements, may allow plants to serve as a simple and inexpensive means to monitor human surroundings for substances such as pollutants, explosives, or chemical agents.