Phosphorus Deficiency and Root Growth: The Role of TOR Signaling in Adaptive Responses.

Phosphorus (P) is a vital macronutrient, yet its bioavailability in soils is often limited, restricting plant growth. In response to P deficiency, plants adapt by reconfiguring root architecture-impeding primary root growth, promoting lateral root formation, and elongating root hairs-to enhance P acquisition. Central to these responses is the Target of Rapamycin Complex 1 (TORC1), a highly conserved master regulator that integrates nutrient, energy, and environmental signals to balance growth and metabolic demands. Recent studies reveal complex interactions between TORC1 and P homeostasis, highlighting TORC1's pivotal role in modulating early root growth. Notably, while early P deficiency impedes root development in an iron (Fe)-independent manner, short-term P deficiency coupled with excess Fe exacerbates this response by inducing oxidative stress, complicating root adaptations. The reciprocal regulation of Fe and P homeostasis, along with TORC1's central role, sheds new light on the dynamic regulation of root plasticity, particularly lateral root development. This review synthesizes recent advances in TORC1-mediated root architecture under P stress and explores how these interconnected pathways can be harnessed to enhance P use efficiency in crops, offering actionable strategies for sustainable agriculture and crop breeding.