Department of Plant Sciences

Iron (Fe) is critical for plant growth. Under conditions of low Fe availability, rice plants induce genes involved in Fe uptake and utilization. Recently, we identified the iron-deficiency-responsive cis-acting elements IDE1 and IDE2, which are bound in a specific manner by IDE-binding factors 1 and 2 (IDEF1 and IDEF2, respectively). IDEF1 and IDEF2 regulate genes related to the Fe-deficiency response. In the present study, we examined the spatial expression patterns of IDEF1 and IDEF2 during the germination, vegetative, and seed-maturation stages by assessing their localization in IDEF1 and IDEF2 promoter–GUS transgenic rice lines. During germination, IDEF1 and IDEF2 were expressed in the endosperm and embryo. In hydroponic culture experiments, the expression patterns of IDEF1 and IDEF2 were similar under both Fe-deficient and Fe-sufficient conditions during the vegetative stage. In leaves, IDEF1 expression was observed in mesophyll cells and in small vascular bundles, whereas IDEF2 was highly expressed in vascular bundles. In root sections, IDEF1 and IDEF2 were highly expressed in secondary roots and inside vascular bundles. IDEF1 was also expressed in pollen from flowers before and after anthesis, in the ovary after fertilization, and in the embryo during seed maturation. IDEF2 was expressed in flowering stage pollen, in immature seeds just after flowering, and in the dorsal vascular region during the late maturation stage. The spatial expression patterns of IDEF1 and IDEF2 partially overlapped with their target genes.