Department of Plant Sciences

Iron is essential for most living organisms and is required for normal plant growth. Plants induce iron utilization systems under conditions of low iron availability, but the molecular mechanisms of this gene regulation system remain largely unknown. We identified the rice transcription factor IDEF1, which specifically binds the iron-deficiency-responsive cis-acting element IDE1. IDEF1 belongs to an uncharacterized branch of the plant-specific transcription factor family ABI3/VP1 and efficiently binds to the CATGC sequence within IDE1. IDEF1 transcripts are constitutively present in rice roots and leaves. Transgenic tobacco plants expressing IDEF1 under the control of the constitutive cauliflower mosaic virus 35S promoter transactivate IDE1-mediated expression only in iron-deficient roots. Transgenic rice plants expressing IDEF1 under the control of the iron-deficiency-inducible IDS2 promoter tolerate iron deficiency in hydroponic culture and calcareous soil. Conversely, transgenic rice plants with repressed IDEF1 expression are susceptible to early stage iron deficiency in hydroponic culture. Expression analysis of these transgenic plants revealed that IDEF1 positively regulates iron-deficiency-induced genes, including the ferrous iron transporter gene OsIRT1 and the iron-deficiency-induced transcription factor gene OsIRO2. These data suggest the presence of a sequential gene regulatory network that functions via novel cis element/trans factor interactions to promote the iron-deficiency response.