Living sensors: Engineering plants to sense and report on their environments.

Plants have long served as natural indicators of environmental conditions, and recent advances in synthetic biology are enabling the design of engineered sentinels - living sensors that can report on abiotic and biotic stressors. This review summarizes recent advances in designing sensor plants, also called phytosensors or sentinel plants, highlighting three major strategies: (1) exploiting native promoter systems responsive to environmental cues, (2) engineering protein-based genetically encoded biosensors that detect specific molecules of interest, and (3) constructing interkingdom signaling networks between plants and microbes to extend sensing capabilities to the rhizosphere. These sense-response modules can be coupled to optical reporters (e.g., fluorescence, bioluminescence, and pigment-based) that enable remote detection via drones and satellite imaging. Continued improvements in promoter design, receptor modularity, and signal visualization technologies are driving the development of robust, field-deployable plant biosensors. Together, these innovations position engineered sensor plants as scalable, self-sustaining sentinels for real-time environmental monitoring and land management.