The tomato fer gene encoding a bHLH protein controls iron-uptake responses in roots

Abstract

Iron deficiency is among the most common nutritional disorders in plants. To cope with low iron supply, plants with the exception of the Gramineae increase the solubility and uptake of iron by inducing physiological and developmental alterations including iron reduction, soil acidification, Fe(II) transport and root-hair proliferation (strategy I). The chlorotic tomato fer mutant fails to activate the strategy I. It was shown previously that the fer gene is required in the root. Here, we show that fer plants exhibit root developmental phenotypes after low and sufficient iron nutrition indicating that FER acts irrespective of iron supply. Mutant fer roots displayed lower Leirt1 expression than wild-type roots. We isolated the fer gene by map-based cloning and demonstrate that it encodes a protein containing a basic helix-loop-helix domain. fer is expressed in a cell-specific pattern at the root tip independently from iron supply. Our results suggest that FER may control root physiology and development at a transcriptional level in response to iron supply and thus may be the first identified regulator for iron nutrition in plants.

The Arabidopsis Mediator subunit MED16 regulates iron homeostasis by associating with EIN3/EIL1 through subunit MED25

“…Iron (Fe)-deficiency induced transcription factor (FIT) is a basic helix-loop-helix (bHLH) family transcription factor induced by iron deficiency at the transcriptional level. The role of FIT is in iron homeostasis, regulating the expression of IRT1 and FRO2 in species of Arabidopsis and tomato (Ling et al, 2002;Colangelo and Guerinot, 2004;Jakoby et al, 2004;Yuan et al, 2005). Yuan et al (2008) and Wang et al (2012) proposed that FIT forms a complex with other iron-deficiencyinduced bHLH transcription factors such as bHLH38, bHLH39, bHLH100 and bHLH101.…”

Iron deficiency-mediated stress regulation of four subgroup Ib BHLH genes in Arabidopsis thaliana

“…FER and FIT share higher sequence similarity with each other rather than with any other known bHLH protein from the two species. FER is required for induction of iron reductase and iron transporter genes in tomato (Ling et al 2002;Bereczky et al 2003;Bauer et al 2004;Li et al 2004). FIT was found essential for the induction of FRO2 upon iron deWciency in Arabidopsis (Colangelo and Guerinot 2004;Jakoby et al 2004) as well as for induction of IRT1 (Jakoby et al 2004).…”

“…One allele has a T-DNA insertion in an exon (Wt-3 = fru-G108), the other allele contains a premature EMS-induced stop codon in an exon (Jakoby et al 2004). Loss of function of FER and FIT resulted in lethal leaf chlorosis due to insuYcient iron uptake in tomato and in Arabidopsis (Ling et al 2002;Colangelo and Guerinot 2004;Jakoby et al 2004). Expression of FER and FIT was induced by low iron supply compared to suYcient and/or generous iron supply suggesting that iron mobilization is controlled by a cascade of transcription factors with FER/FIT genes being part of it.…”

Iron homeostasis in plants: when transcription affects translocation

“…It was demonstrated that long distance signaling from the shoot to the roots is key to regulating iron uptake in the roots [5]. However, there is still a significant gap and virtually no progress has been made in our understanding on how plants sense their iron status and how the signals are transduced across the plant toward the root cells to induce or repress the expression of key genes involved in iron homeostasis such as the genes coding for ferric reductases (FRO) or the iron transporters (IRT1, IRT2).As pointed out by Chen et al in their article of this issue of Cell Research [6], there are only two accounts in the literature describing transcription factors involved in the regulation of iron metabolism in plants [7,8]. Therefore the work reported by Chen et al is of significant importance in the quest to identifying key regulatory genes involved in iron homeostasis.…”

“…As pointed out by Chen et al in their article of this issue of Cell Research [6], there are only two accounts in the literature describing transcription factors involved in the regulation of iron metabolism in plants [7,8]. Therefore the work reported by Chen et al is of significant importance in the quest to identifying key regulatory genes involved in iron homeostasis.…”