The TORC-SnRK Axis: An Integrative Signaling Framework Balancing Growth and Stress Responses in Plants

As sessile organisms, plants must continuously balance growth and stress adaptation in response to fluctuating environments. This balance is largely governed by two evolutionarily conserved kinase systems, the Target of Rapamycin Complex (TORC) and Snf1-Related Kinases (SnRKs). Under favorable conditions, plants adopt a "growth mode" in which sufficient nutrients, energy, and growth-promoting hormones activate TORC to drive anabolic metabolism, cell proliferation, and biomass accumulation. By contrast, under adverse conditions such as energy limitation, nutrient deprivation, and other environmental stresses, plants shift to an "adaptation mode" in which stress-associated cues, including low ATP, stress hormones (e.g., ABA), and Ca²⁺ transients activate distinct SnRK modules (SnRK1, SnRK2, and SnRK3/CIPKs) to promote catabolic reprogramming and enhance stress tolerance. Recent advances support a unifying model in which TORC and SnRKs reciprocally regulate each other, enabling plants to switch between growth and adaptation. In this review, we summarize how diverse growth-associated signals converge on TORC and how stress-specific signaling inputs selectively activate SnRK modules, and we highlight recent progress in elucidating the molecular mechanisms underlying TORC-SnRK crosstalk. We propose that the TORC-SnRK axis serves as a central signaling module that integrates energy, hormonal, and Ca²⁺ signals to coordinate growth and stress responses. This conceptual framework facilitates a mechanistic understanding on how plants optimize fitness in fluctuating environments and offers potential strategies for improving crop performance through targeted manipulation of this regulatory network.