Proposed regulatory network for the induction of Fe-deficiency-responsive genes via IDEF1, IDEF2, and OsIRO2. Under Fe-deficient conditions, IDEF1 and IDEF2 transactivate the expression of Fe-deficiency-responsive genes by binding to the IDE1-like and IDE2-like elements, respectively [27, 45]. OsIRO2, which is induced by Fe deficiency and is positively regulated by IDEF1, binds to the CACGTGG element to activate another subset of Fe-deficiency-responsive genes, including two transcription factor genes: OsNAC4 and the AP2 domain-containing gene. These transcription factors may then regulate Fe-deficiency-responsive genes lacking IDEs and CACGTGG in their promoter regions . The induced expression of IDEF1 in transgenic rice plants would effectively strengthen the overall regulatory pathway to confer tolerance to Fe deficiency.