Understanding Crosstalk Between Phosphate and Immune-Related Signaling in Rice and Arabidopsis Through Live Imaging of Phosphate Levels

Phosphate (Pi) is a vital macronutrient for plant growth and development, and precise monitoring of its cellular dynamics is essential to understanding Pi homeostasis and its interaction with stress responses. Genetically encoded FRET-based biosensors such as FLIPPi enable real-time, non-invasive visualization of cytosolic Pi levels in living tissues. In this study, <i>Arabidopsis</i> and rice lines expressing a FLIPPi biosensor were used to monitor cytosolic Pi dynamics in root epidermal cells. Sensor functionality was confirmed by measuring FRET responses to graded Pi supplies, revealing a consistent reduction in FRET ratios with increasing Pi concentrations, reflecting elevated cytosolic Pi levels. Comparisons with a Pi-insensitive FLIPPi variant confirmed the specificity of the observed changes. Furthermore, live imaging demonstrated rapid and dynamic alterations in cytosolic Pi upon treatment with defense-related hormones and elicitors of immune responses supporting a link between Pi signaling and plant immunity. Finally, the application of phosphite, an analog of Pi, altered Pi dynamics in both <i>Arabidopsis</i> and rice, suggesting an interference with Pi accumulation. Collectively, our findings establish FLIPPi as a reliable tool for in vivo monitoring of Pi in <i>Arabidopsis</i> and rice plants, the model systems for studies in dicotyledonous and monocotyledonous species, respectively.