No energy, no defense: Metabolic input shapes defense signaling

Mounting signaling outputs in response to environmental changes is energetically demanding and metabolically costly. Therefore, cellular metabolic status is expected to play an important role in regulating signaling pathways. However, compared with the well-developed research on how receptors detect environmental cues and initiate signaling, the importance of cellular resources in shaping signaling outputs has been less widely recognized. Defense signaling, in particular, triggers multiple outputs and imposes a substantial burden on cellular resources. Accordingly, defense responses are markedly attenuated under nutrient-limited conditions. Plants actively reallocate resources during defense, coordinating growth suppression with defense prioritization. Moreover, cellular resources are not merely a supportive foundation for defense responses; metabolic status itself can also be translated into molecular signals that regulate defense signaling. Recent findings have begun to elucidate the molecular mechanisms underlying these processes. This review thus focuses on how cells allocate cellular resources to sustain defense and how resource status is integrated into signaling pathways at the molecular level as a regulatory input.