Quantifying plant biology with fluorescent biosensors

Plant biology is undergoing a spatial omics revolution, but these approaches are limited to snapshots of a plant's state. Direct, genetically encoded fluorescent biosensors complement the omics approaches, giving researchers tools to assess energetic, metabolic, and signaling molecules at multiple scales, from fast subcellular dynamics to organismal patterns in living plants. This review focuses on how biosensors illuminate plant biology across these scales and the major discoveries to which they have contributed. We also discuss the core principles and common pitfalls affecting biosensor engineering, deployment, imaging, and analysis to help aspiring biosensor researchers. Innovative technologies are driving forward developments both biological and technical with implications for synergizing biosensor research with other approaches and expanding the scope of in vivo quantitative biology.