Abstract
Iron (Fe) homeostasis is essential for plant growth and development, and it is strictly regulated by a group of transcriptional factors. Iron-related transcription factor 3 (OsIRO3) was previously identified as a negative regulator for Fe deficiency response in rice. However, the molecular mechanisms by which OsIRO3 regulate Fe homeostasis is unclear. Here, we report that OsIRO3 is essential for responding to Fe deficiency and maintaining Fe homeostasis in rice. OsIRO3 is expressed in the roots, leaves, and base nodes, with a higher level in leaf blades at the vegetative growth stage. Knockout of OsIRO3 resulted in a hypersensitivity to Fe deficiency, with severe necrosis on young leaves and defective root development. The iro3 mutants accumulated higher levels of Fe in the shoot under Fe-deficient conditions, associated with upregulating the expression of OsNAS3, which lead to increased accumulation of nicotianamine (NA) in the roots. Further analysis indicated that OsIRO3 can directly bind to the E-box in the promoter of OsNAS3. Moreover, the expression of typical Fe-related genes was significantly up-regulated in iro3 mutants under Fe-sufficient conditions. Thus, we conclude that OsIRO3 plays a key role in responding to Fe deficiency and regulates NA levels by directly, negatively regulating the OsNAS3 expression.
Highlights
Iron (Fe) is an indispensable micronutrient for plants and animals
To investigate the tissue-specific OsIRO3 expression pattern, we examined its levels in different tissues from 6-week-old rice plants
OsIRO3 has been reported as a negative regulator in response to Fe deficiency only based on the functional analysis of OsIRO3 overexpression lines [29]
Summary
Iron (Fe) is an indispensable micronutrient for plants and animals. It acts as a cofactor for a number of enzymes and plays an essential role in many metabolic processes [1]. Fe deficiency is one of the most prevalent nutrient deficiencies in the world; it affects more than one third of the global population [2]. Plants, which are the major Fe sources for humans, take up inorganic Fe from the soil. Fe is abundantly present in the earth’s crust, its bioavailability is very low due to the insolubility of inorganic Fe, especially in calcareous soils, which account for about 30% of the world’s cultivated soils [3]. Disclosing the mechanism underlying Fe homeostasis in plants is important to human health
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