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The uri Mutant Does Not Mount an Fe Deficiency Response. To find genes required for Fe deficiency signaling in A. thaliana, we generated a transgenic line carrying a luciferase gene driven by the IRT1 promoter (pIRT1: LUC) and screened for mutants that do not induce the reporter gene under Fe-deficient growth conditions. Leaf chlorosis was also evaluated, because candidate mutants would phenocopy the irt1 mutant if the induction of endogenous IRT1 is defective (22–24). One recessive mutant was isolated and named uri. The uri mutant failed to induce the IRT1 promoter-driven luciferase gene and developed leaf chlorosis on Fe-deficient medium (Fig. 1A). The uri mutant was seedling lethal in soil, but this phenotype could be reversed by feeding the plants ferric sodium ethylenediamine-N, N’-bis (2-hydroxyphenylacetic acid)(FeEDDHA)(Fig. 1A). Next, we measured the abundance of IRT1 transcript …