Blue light promotes root iron acquisition via a shoot CRY-HY5 signaling module in Arabidopsis.

Iron (Fe) is an essential element for almost all living organisms, and its deficiency severely impacts crop productivity and human health. While the mechanisms underlying iron uptake and accumulation are well studied, the role of light in modulating iron homeostasis remains poorly understood. In this study, we report that blue light enhances iron accumulation thereby positively regulating iron homeostasis in Arabidopsis thaliana. Under iron-deficient (-Fe) conditions, root elongation is specifically promoted by blue light, but not by red light. We further revealed that light perceived by shoots is required for optimum iron accumulation and for iron deficiency-induced increase in root length. The transcription factor HY5 (ELONGATED HYPOCOTYL 5) mediates these blue light-driven responses. The hy5 mutant showed reduced root elongation under -Fe conditions as well as iron accumulation under blue light as compared to wild-type plants. Further we report that CRY1 and CRY2 are the photoreceptor that acts as a connecting link between blue light and HY5 to regulate iron uptake in Arabidopsis. Overall, our work reveals a new regulatory mechanism and offers potential insights into optimizing light conditions to enhance iron accumulation and improve the nutritional quality of crops. Summary Blue light, acting via cryptochromes and the transcription factor HY5, positively regulates iron accumulation in Arabidopsis, revealing a new mechanism for light mediated regulation of iron homeostasis in plants.