From Fuel to Fortress: The Defensive Side of Plant Sugars

The carbohydrate status of plants encompasses both energy resources (sugars and starch) and structural components of the cell wall, shaped by photosynthesis, environmental stress, and growth demands. Carbohydrates are spatially and temporally regulated through subcellular compartmentation, source–sink transitions, and shifts in sugar composition, all of which critically influence plant health and performance.Beyond their metabolic functions, soluble sugars such as sucrose, glucose, and fructose act as key signaling molecules and that integrate carbohydrate metabolism, transport, and energy status with plant defense responses. Dynamic regulation of sugar transporters and sucrose-cleaving enzymes enables rapid adjustment of carbohydrate allocation, providing both energetic resources and regulatory signals during biotic stress. In addition, the plant cell wall contributes to immunity not only as a physical barrier but also as a dynamic source of immune-eliciting oligosaccharides, thereby linking carbohydrate status to pattern-triggered immunity.This review synthesizes recent advances in understanding how carbohydrates coordinate metabolic, signaling, and structural defenses during plant interactions with pathogens and herbivores. Particular emphasis is placed on sugar-mediated priming of immune responses and the emerging potential of sugars and oligosaccharides as sustainable tools for crop protection and enhanced plant resilience.