Phosphate Deficiency Attenuates SnRK1 Activity to Modulate the Phosphate Starvation Response in Arabidopsis thaliana
Phosphate starvation requires extensive metabolic and developmental reprogramming, yet how this response is coordinated with cellular energy status remains poorly understood. The energy sensor SnRK1 regulates plant growth and metabolism in response to energy availability, but its contribution to the regulation and deployment of the phosphate starvation response (PSR) remains unclear. To address this, we combined physiological, proteomic and metabolomic analyses with genetic manipulation of SnRK1 activity in Arabidopsis thaliana to determine how SnRK1 influences plant responses to phosphate starvation. We found that phosphate starvation reduced SnRK1 activity and activation-loop (T-loop) phosphorylation, while altering SnRK1 activity changed the timing and magnitude of physiological, proteomic and metabolic responses to phosphate limitation. Reduced SnRK1 activity was generally associated with earlier and stronger deployment of PSR-associated responses, whereas increased SnRK1 activity delayed or attenuated several components of the response. These effects were tissue- and time-dependent and were accompanied by distinct metabolic configurations. Our findings support a model in which SnRK1 acts as a quantitative metabolic brake on the PSR, coordinating the metabolic investment required for phosphate-starvation adaptation with growth.