Iron-Mediated Control of the Basic Helix-Loop-Helix Protein FER, a Regulator of Iron Uptake in Tomato

Abstract

Root iron mobilization genes are induced by iron deficiency downstream of an unknown signaling mechanism. The FER gene, encoding a basic helix-loop-helix domain protein and putative transcription factor, is required for induction of iron mobilization genes in roots of tomato (Lycopersicon esculentum). To study upstream regulatory events of FER action, we examined the control of FER gene and FER protein expression in response to iron nutritional status. We analyzed expression of the FER gene and FER protein in wild-type plants, in mutant plants with defects in iron uptake regulation, and in 35S transgenic plants that overexpressed the FER gene. An affinity-purified antiserum directed against FER epitopes was produced that recognized FER protein in plant protein extracts. We found that the FER gene and FER protein were consistently downregulated in roots after generous (100 mM, physiologically optimal) iron supply compared to low (0.1 mM) and sufficient (10 mM) iron supply. FER gene and FER protein expression were also occasionally down-regulated at sufficient compared to low iron supply. Analysis of FER protein expression in FER overexpression plants, as well as cellular protein localization studies, indicated that FER was down-regulated by high iron at the posttranscriptional level. The FER protein was targeted to plant nuclei and showed transcriptional activation in yeast (Saccharomyces cerevisiae). FER protein regulation in the iron accumulation mutant chloronerva indicated that FER protein expression was not directly controlled by signals derived from iron transport. We conclude that FER is able to affect transcription in the nucleus and its action is controlled by iron supply at multiple regulatory levels.

Systems and Trans-System Level Analysis Identifies Conserved Iron Deficiency Responses in the Plant Lineage

“…In higher plants, a number of transcription factors have been identified as components of the iron signaling response, including FIT1/FER, PYE, bHLH115, and ILR3 (Ling et al, 2002;Colangelo and Guerinot, 2004;Brumbarova and Bauer, 2005;Bauer et al, 2007;Dinneny et al, 2008;Jeong and Guerinot, 2009;Long et al, 2010). In addition, there is a posttranslational component involving an E3 ubiquitin ligase BTS (Long et al, 2010).…”

Ethylene involvement in the regulation of the H+-ATPase CsHA1 gene and of the new isolated ferric reductase CsFRO1 and iron transporter CsIRT1 genes in cucumber plants

“…The Arabidopsis FRU protein (also named FIT1), a homolog of the tomato FER protein, is necessary for the activation of the ferric reductase AtFRO2 [7,18], the H + -ATPase AtAHA7 [7] and the iron transporter AtIRT1 [18] gene expression, although in the regulation of the iron transporter there is discrepancy between the results of Colangelo and Guerinot [7] and those of Jakoby et al [18]. LeFER and AtFRU expression is induced in roots in response to Fe deficiency [1,5,7,18]. Very recently, Lucena et al [23] have shown that ethylene could regulate FRO and IRT gene expression by affecting the FER (or FERlike) gene activity.…”

AtbHLH29 of Arabidopsis thaliana is a functional ortholog of tomato FER involved in controlling iron acquisition in strategy I plants

“…The ferric chelate reductase LeFRO1 and the metal transporter LeIRT1 and LeNRAMP1 are proposed as main func- in tomato [33] and AtbHLH29 in Arabidopsis [24,25] has already been observed. In Addition to AtbHLH29 and FER, the posttranscriptional regulation of the ferric-chelate reductase AtFRO2 and the Fe(II)-transporter AtIRT1 was also reported [14,34].…”