This study introduces BioLumiPi, a novel, low-cost, and non-invasive biosensor plant, engineered by combining a phosphate (Pi) deficiency-induced promoter with a fungal bioluminescence system in tobacco. BioLumiPi plants emit light that accurately reflects endogenous Pi deficiency and responds specifically to Pi levels. Coupled with deep learning analysis, this technology offers a proof-of-concept strategy for real-time visualisation and prediction of nutrient stress to optimise fertiliser application and advance sustainable agriculture.