Light-mediated balances and trade-offs in plant energy and resource management

Light is a central environmental signal that coordinates plant development, metabolism, and stress responses. By integrating external cues with internal programs, plants balance growth and resource allocation to adapt to fluctuating environments. Light-regulated signalling cascades drive morpho-physiological adaptations for optimized light capture, tuning photosynthetic efficiency, and source-sink dynamics. Key transcriptional hubs, regulated by master transcription factors such as ELONGATED HYPOCOTYL 5 (HY5), PHYTOCHROME INTERACTING FACTORS (PIFs), and GOLDEN 2-LIKE transcription factors (GLKs) coordinate photosynthesis, growth, and defence responses, driving adjustments and imposing balances for adaptation to shade, variable light, and stress. In addition to photosynthetic energy production, light signalling pathways influence carbon and nitrogen metabolism, leading to sugar allocation, starch turnover, and nutrient utilization-balancing trade-offs between growth, energy storage, and stress responses. Emerging evidence shows that light signalling pathways intersect with energy-monitoring cascades regulated by TARGET OF RAPAMYCIN (TOR), trehalose-6-phosphate (T6P), and SUCROSE NON-FERMENTING-RELATED PROTEIN KINASE 1 (SnRK1), linking the plant's energy status to growth, immunity, and stress resilience. Sugar concentration and light signals can also jointly regulate responses to both biotic and abiotic stress, with TOR acting as a central integration hub for environmental and metabolic signals, including transcriptional and translational mechanisms. This review synthesizes our current understanding on the interplay between light and TOR-mediated networks in energy production and allocation, while highlighting knowledge gaps that limit translational potential for improving plant productivity and resilience.