A Novel NAC Transcription Factor, IDEF2, That Recognizes the Iron Deficiency-responsive Element 2 Regulates the Genes Involved in Iron Homeostasis in Plants

Yuko Ogo,Takanori Kobayashi,Reiko Nakanishi Itai,Hiromi Nakanishi,Yusuke Kakei,Michiko Takahashi,Seiichi Toki,Satoshi Mori,Naoko K Nishizawa

doi:10.1074/jbc.m708732200

Yuko Ogo, Takanori Kobayashi + Show 7 more

Open Access

https://doi.org/10.1074/jbc.m708732200

Copy DOI

Abstract

Iron is essential for most living organisms, and thus iron deficiency poses a major abiotic stress in crop production. Plants induce iron utilization systems under conditions of low iron availability, but the molecular mechanisms of gene regulation under iron deficiency remain largely unknown. We identified a novel transcription factor of rice and barley, IDEF2, which specifically binds to the iron deficiency-responsive cis-acting element 2 (IDE2) by yeast one-hybrid screening. IDEF2 belongs to an uncharacterized branch of the NAC transcription factor family and exhibits novel properties of sequence recognition. An electrophoretic mobility shift assay and cyclic amplification and selection of targets experiment revealed that IDEF2 predominantly recognized CA(A/C)G(T/C)(T/C/A)(T/C/A) within IDE2 as the core-binding site. IDEF2 transcripts are constitutively present in rice roots and leaves. Repression of the function of IDEF2 by the RNA interference (RNAi) technique and chimeric repressor gene-silencing technology (CRES-T) caused aberrant iron homeostasis in rice. Several genes up-regulated by iron deficiency, including the Fe(II)-nicotianamine transporter gene OsYSL2, were less induced by iron deficiency in the RNAi rice of IDEF2, suggesting that IDEF2 is involved in the regulation of these genes. Many genes with repressed expression in IDEF2 RNAi rice possessed the IDEF2-binding core sites in their promoters, and the flanking sequences were also highly homologous to IDE2. IDEF2 bound to OsYSL2 promoter region containing the binding core site, suggesting direct regulation of OsYSL2 expression. These results reveal novel cis-element/trans-factor interactions functionally associated with iron homeostasis.

Highlights

We have demonstrated that OsIRO2, the iron deficiencyinducible bHLH transcription factor in rice, regulates the strategy II-based iron-deficiency response by inducing the related genes [19, 20]
IDEF2 induced gene expression even in the absence of activation domain (AD) in yeast cells carrying the lacZ gene fused to iron deficiency-responsive cis-acting element 2 (IDE2)-IDE1 ϫ 2 or IDE2 ϫ 3 (Fig. 1c), indicating that IDEF2 works as a transcriptional activator
The genes under regulation of IDEF2 were identified by expression analysis using IDEF2 RNA interference (RNAi) rice

Summary

Introduction

We have demonstrated that OsIRO2, the iron deficiencyinducible bHLH transcription factor in rice, regulates the strategy II-based iron-deficiency response by inducing the related genes [19, 20]. Expression levels of IDEF2 and IDEF2 ORF-SRDX in iron-deficient roots of these transgenic rice lines were confirmed by Northern blot analysis (Fig. 5 and data not shown).

Results

Conclusion