Impact of photoperiod and micronutrients on rice gene networks, phytochrome activity, and grain quality under low light

Light availability is a decisive environmental factor influencing crop productivity, with rice (Oryza sativa L.) being particularly sensitive to suboptimal illumination. Low light (LL) stress, often caused by prolonged cloud cover, canopy shading, or high planting density, impairs photosynthetic efficiency and disrupts carbon assimilation, ultimately limiting yield potential. In rice, the effects of LL are further modulated by photoperiod sensitivity and micronutrient availability, which together influence phenological progression, reproductive development, and grain quality. This research review synthesizes advances in understanding the morphological, physiological, metabolic, and molecular responses of rice to LL stress within the context of photoperiodic regulation and micronutrient dynamics. Molecular investigations reveal that LL triggers extensive transcriptional reprogramming involving light-harvesting complexes, circadian and photoperiodic gene networks, carbohydrate metabolism, hormonal crosstalk, and micronutrient-responsive pathways. Integrative multi-omics approaches encompassing transcriptomics, proteomics, and metabolomics are beginning to unravel the regulatory networks and adaptive mechanisms underpinning LL tolerance. The manuscript also discusses mitigation strategies, including breeding for LL-tolerant and photoperiod-flexible genotypes, enhancing micronutrient nutrition, and optimizing canopy management to maximize light interception. By consolidating mechanistic insights across biological scales, this work identifies critical research gaps, particularly in genotype-by-environment-by-management interactions and the co-occurrence of LL with other abiotic stresses. Addressing these challenges will be central to safeguarding rice productivity and quality in light-limited environments under variable photoperiods and nutrient regimes.