Dual regulation of iron deficiency response mediated by the transcription factor IDEF1.

Higher plants respond to fluctuating Fe availability by regulating the expression of genes involved in Fe homeostasis. Transcriptional responses to Fe deficiency in plants are mediated via various interactions between cisacting elements and trans-acting factors. The transcription factor IDEF1 regulates the response to Fe deficiency in (rice) by recognizing the CATGC sequence within the Fe deficiency-responsive cis-acting element IDE1. We recently presented evidence that mediates two-phase responses to Fe deficiency. During the early stages of Fe deficiency, the majority of known Fe uptake/utilization-related genes are positively regulated by IDEF1. In subsequent stages, IDEF1-mediated regulation of these Fe uptake/utilization-related genes are less obvious. In turn, expression of several Fe deficiency-induced genes encoding late embryogenesis abundant proteins is increasingly regulated by IDEF1 at the subsequent stages. We propose a dual function of IDEF1 for Fe deficiency response, namely, (1) the coordinated transactivation of Fe utilization-related genes via CATGC-containing IDE1-like elements, especially at the early stage, and (2) the transactivation of seed maturation-related genes via RY elements, especially during the subsequent stages of Fe deficiency. appears to have evolved to mediate an interface between Fe deficiency-inducible and seed maturation-related gene expression.