Figure 2. Role of ethylene and auxin in the spatial regulation of IRT1 expression. (A-X) GUS staining of representative plants expressing the IRT1pro:GUS cassette in Col-0 and snx1–2 genetic background. Treatments were made as indicated. The mock treatment was iron-deficient Hoagland medium with 0.1% ethanol. For each genotype and treatment, three images are shown: a seedling overview and two magnifications of regions indicated with rectangles on the overview image. (Y) Ethylene and auxin play opposing roles when defining the expression of IRT1 along the root depending on the plant iron demands. Under sufficient iron supply or mild iron deficiency, auxin dominates over ethylene causing IRT1 expression in the extremities of the root (left). The balance between the two hormones leads to an almost continuous IRT1 presence when iron is insufficient (center). Under severe iron limitation, dominant ethylene presence causes the concentration of IRT1 expression in the early differentiation zone (right).