Mechanisms of low light stress in rice: current insights and future directions

Light has a significant impact on rice growth and development. It is essential for photosynthesis and plays a central role in coordinating photoperiodism, plant architecture, and yield. Countries with the highest rice yields are typically those receiving the most solar radiation. However, long stretches of the monsoonal wet season in South and Southeast Asia including India—particularly eastern and northeastern regions—as well as China, hamper rice productivity. During this period, rice crops receive only 800–900 h of bright sunshine, compared to the required 1,500 h, resulting in 30–60% yield reductions compared to the dry season. Although the exact mechanism of light-regulated gene expression is not yet fully understood, significant physiological, anatomical, biochemical, and agronomic changes have been observed under low light (LL) stress. Morphologically, LL stress leads to plants with increased height, leaf area and angle, but reduced tiller number and underdeveloped root arhitecture. Physiologically, it causes reduced chlorophyll a/b ratios and suppresses Rubisco activity, leading to lower carbon fixation. Biochemically, it alters antioxidant enzyme activities and reduces starch accumulation, which contributes to chalky grains and a higher glycemic index.At the molecular level, LL stress downregulates key genes such as OsCESA1, OsCESA3, and PhyA, affecting cell wall development and chlorophyll retention. These genetic responses disrupt normal grain filling and reduce yield quality. This review brings together current insights into these multi-layered responses to LL stress in rice. The goal is to better understand the complex interactions between genes, hormones, and plant physiology. These findings are critical for informing breeding programs aimed at developing LL-resilient rice cultivars and improving productivity in regions increasingly affected by cloudy, low-radiation environments due to climate change.