Abstract
Iron (Fe) is an essential element required for plant growth and development. Under Fe-deficientconditions, plants have developed two distinct strategies (designated as strategy I and II) to acquire Fe from soil. As a graminaceous species, rice is not a typical strategy II plant, as it not only synthesizes DMA (2′-deoxymugineic acid) in roots to chelate Fe3+ but also acquires Fe2+ through transporters OsIRT1 and OsIRT2. During the synthesis of DMA in rice, there are three sequential enzymatic reactions catalyzed by enzymes NAS (nicotianamine synthase), NAAT (nicotianamine aminotransferase), and DMAS (deoxymugineic acid synthase). Many transporters required for Fe uptake from the rhizosphere and internal translocation have also been identified in rice. In addition, the signaling networks composed of various transcription factors (such as IDEF1, IDEF2, and members of the bHLH (basic helix-loop-helix) family), phytohormones, and signaling molecules are demonstrated to regulate Fe uptake and translocation. This knowledge greatly contributes to our understanding of the molecular mechanisms underlying iron deficiency responses in rice.
Highlights
Iron (Fe) is one of the key micronutrients required for various metabolic processes in plants [1,2]
We summarize the recent progress involved in the Fe signaling networks and homeostasis in rice, and the detailed knowledge of regulatory roles of phytohormones and messenger molecules in Fe homeostasis
Kobayashi et al found that OsbHLH58 and OsbHLH59 are two positive regulators of Fe responses, such that the knockout of these two transcription factors decreases the expression of Fe deficiency response genes and impairs the tolerance of rice plants to Fe deficiency treatments [46]
Summary
Iron (Fe) is one of the key micronutrients required for various metabolic processes in plants [1,2]. Rice is equipped with strategy I to acquire Fe2+, which is mediated by two Fe2+ transporters, OsIRT1 and OsIRT2, in root cells [18]. This is conceivable because rice and its wild relatives need to adapt to waterlogged wetlands, where most iron elements exist as Fe2+ due to the low redox potential [18,19]. CO2 due to anthropological activities, which will aggravate micronutrient deficiencies in human nutrition in rice-dependent countries [23,24,25] To address these problems, we need to biofortify Fe concentrations in rice grains by means of genetic breeding, which relies on determining the mechanisms underlying Fe deficiency responses in rice.
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