Decoding the Plant Nutrient Continuum: Regulatory Logic from Deficiency to Sufficiency and Toxicity

Plants experience nutrient availability as a dynamic continuum spanning deficiency, physiological sufficiency, and toxic excess. However, nutrient responses are commonly interpreted as discrete states, limiting understanding of how plants integrate signals across gradients. Here, we synthesize molecular, cellular, and systems-level evidence to propose a unified regulatory framework in which nutrient signaling can be interpreted as operating within a metabolically constrained, context-dependent regulatory system. Nutrient perception emerges from integration of membrane-localized transceptors, intracellular metabolic sensors, Ca2+ and redox-associated signaling, and systemic pathways. These inputs converge on central regulatory hubs, particularly the TOR-SnRK1 axis, linking nutrient availability with carbon-energy balance. Downstream transcriptional networks, including NLPs, SPX-PHR modules, NIGT1/HRS1 repressors, and FIT-centered systems, translate nutrient and metabolic status into coordinated gene expression. Post-transcriptional and post-translational mechanisms further constrain system behavior, particularly under nutrient excess. Collectively, this synthesis supports a continuum-based model in which nutrient responses are governed by integrated regulatory networks rather than discrete pathways. This framework provides a foundation for linking molecular regulation with whole-plant physiology and for improving nutrient use efficiency and resilience under variable environments, and provides a predictive framework for integrating molecular regulation with crop performance.