The rice bHLH protein OsIRO2 is an essential regulator of the genes involved in Fe uptake under Fe‐deficient conditions

• Published in: The Plant journal : for cell and molecular biology Vol. 51; no. 3; pp. 366 - 377
• Main Authors: Ogo, Yuko, Nakanishi Itai, Reiko, Nakanishi, Hiromi, Kobayashi, Takanori, Takahashi, Michiko, Mori, Satoshi, Nishizawa, Naoko K.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.08.2007; Blackwell Science
• Subjects: Absorption. Translocation of ions and substances. Permeability; Agronomy. Soil science and plant productions; Azetidinecarboxylic Acid - analogs & derivatives; Azetidinecarboxylic Acid - metabolism; Basic Helix-Loop-Helix Transcription Factors - genetics; Basic Helix-Loop-Helix Transcription Factors - metabolism; basic helix‐loop‐helix; Biological and medical sciences; Botany; Caulimovirus - genetics; Economic plant physiology; Fundamental and applied biological sciences. Psychology; Gene expression; Gene Expression Profiling; Gene Expression Regulation, Plant; Genes, Plant; Homeostasis - genetics; Iron; Iron - metabolism; Iron Chelating Agents - metabolism; iron‐deficiency‐responsive elements; microarray; Molecular biology; mugineic acid family phytosiderophores; Nutrition. Photosynthesis. Respiration. Metabolism; Oligonucleotide Array Sequence Analysis; Oryza - genetics; Oryza - metabolism; Oryza sativa; Plants, Genetically Modified; Promoter Regions, Genetic; Rice; RNA Interference; iron-deficiency-responsive elements; basic helix-loop-helix; Root; Secretion; Hypersensitivity; EC 2.5.1.43; mugineic acid family phytosiderophores; rice; Stress; Phytosiderophore; microarray; Gene; iron; Transcription factor
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313X.2007.03149.x

Summary Iron (Fe) deficiency is a major abiotic stress in crop production. Although responses to Fe deficiency in graminaceous plants, such as increased production and secretion of mugineic acid family phytosiderophores (MAs), have been described, the gene regulation mechanisms related to these responses are largely unknown. To elucidate the regulation mechanisms of the genes related to Fe acquisition in graminaceous plants, we characterized the Fe‐deficiency‐inducible basic helix‐loop‐helix transcription factor OsIRO2 in rice. In yeast cells, OsIRO2 functioned as a transcriptional activator. In rice, overexpression of OsIRO2 resulted in increased MAs secretion, whereas repression of OsIRO2 resulted in lower MAs secretion and hypersensitivity to Fe deficiency. Northern blots revealed that the expression of the genes involved in the Fe(III)–MAs transport system was dependent on OsIRO2. The expression of the genes for nicotianamine synthase, a key enzyme in MAs synthesis, was notably affected by the level of OsIRO2 expression. Microarray analysis demonstrated that OsIRO2 regulates 59 Fe‐deficiency‐induced genes in roots. Some of these genes, including two transcription factors upregulated by Fe deficiency, possessed the OsIRO2 binding sequence in their upstream regions. OsIRO2 possesses a homologous sequence of the Fe‐deficiency‐responsive cis‐acting elements (IDEs) in its upstream region. We propose a novel gene regulation network for Fe‐deficiency responses, including OsIRO2, IDEs and the two transcription factors.