Figure 1.

Overview of the role of ethylene on the regulation of morphological and physiological responses to Fe deficiency in Strategy I species. Ethylene, through the activation of the transcription factors FIT (FER), bHLH38 and bHLH39, can up-regulate the expression of FRO (ferric reductase), IRT (iron transporter) and flavin synthesis genes, thus increasing ferric reductase activity, Fe²⁺ uptake and flavin synthesis. Similarly, ethylene, through FIT (FER), can up-regulate AHA (H⁺-ATPase) genes, thus causing acidification, and activate the MYB72 transcription factor, which in turn up-regulates genes related to phenolics synthesis. Moreover, MYB72 activates the β-glucosidase BGLU42 and the phenolic efflux transporter ABCG37, both being implicated in the secretion of phenolic compounds. Ethylene has also been implicated in the development of different morphological responses, such as subapical root hairs, root epidermal transfer cells and cluster roots. For the development of these morphological responses, FIT (FER) could indirectly act by affecting ethylene synthesis, through the upregulation of MTK and SAMS (see Figure 3).