Comparative Spatiotemporal Regulation of Iron and Zinc Transporters in Developing Tissues of Temperate Rice Genotypes

Hidden hunger (micronutrient deficiency) contributes majorly for poor mental and physical health for every age group and gender across the world. Here we integrated rice grain ionome with high resolution tissue and developmental stage specific transcriptomic to elucidate the molecular basis of Fe/Zn accumulation in two contrasting temperate rice genotypes: the high mineral pigmented genotype Zag-V9 (20.53 ppm Fe and 53.41 ppm Zn in its husked grains) and the low-mineral white-grained genotype GS-74 (13.40 ppm Fe and 23.71 ppm Zn in its husked grains). Among 498 identified transporter gene, major Fe/Zn transporter families, including ZIP/IRT, YSL, NRAMP, HMA, NAS, VIT, ZIFL, TOM/NAAT and ABC transporters, displayed significantly stronger induction in Zag-V9, particularly during reproductive satge. During grain filling, 195 transporter genes (69.1%) were upregulated in Zag-V9 compared with only 58 (31%) in GS-74, whereas GS-74 showed predominant transcriptional repression (129 genes; 69%). Integrated regulatory network analysis further revealed enhanced activation of bHLH, WRKY, NAC, MYB, ERF and bZIP transcription factors together with enrichment of pathways associated with metal homeostasis, photosynthesis, carbon metabolism, redox regulation and energy-dependent transport. This work provides one of the first comprehensive spatiotemporal regulatory frameworks integrating ionomic validation, developmental transcriptomics and transporter network biology in temperate rice and identifies key candidate genes-including OsYSL2, OsYSL6, OsZIP6, OsNRAMP5, OsNAS1 and HMA3 family transporters-together with their upstream transcriptional regulators as promising targets for genomics-assisted breeding, genome editing and next-generation biofortification strategies to combat global hidden hunger.