Abstract
Iron is an essential nutrient for all plants. However, terrestrial plants often suffer from iron deficiency in alkaline soil due to its extremely low solubility. Alkaline soil accounts for about 30% of all cultivated ground in the world. Plants have evolved two distinct strategies, I and II, for iron uptake from the soil. Dicots and non-graminaceous monocots use Strategy I, which is primarily based on the reduction of iron(III) to iron(II) and the uptake of iron(II) by the iron-regulated transporter, IRT1. In contrast, graminaceous plants use Strategy II to efficiently acquire insoluble iron(III). Strategy II comprises the synthesis and secretion of iron-chelating phytosiderophores, such as mugineic acids and the Yellow Stripe 1 transporter proteins of the iron(III)-phytosiderophore complex. Barley, which exhibits the highest tolerance to iron deficiency in alkaline soil among graminaceous plants, utilizes mugineic acids and the specific iron(III)-mugineic acids transporter, HvYS1. In this study, we established the transgenic plant Petunia hybrida, which originally had only Strategy I, by introducing the HvYS1 transporter gene derived from barley. When the transgenic plants were grown hydroponically in media containing the iron(III)-2′-deoxymugineic acid complex, free 2′-deoxymugineic acid and its iron(III) complex were detected in the root extract of the transgenic plant by electrospray ionization-Fourier transform-ion cyclotron resonance mass spectrometry. The growth of the transgenic petunia was significantly better than that of the control host in alkaline conditions. Consequently, the transgenic plant acquired a significantly enhanced tolerance to alkaline hydroponic media in the presence of the iron(III)-2′-deoxymugineic acid complex. Furthermore, the flower color of the transgenic plant deepened. The results showed that iron-phytosiderophore complexes and their transporters can potentially be utilized to overcome the worldwide iron uptake problems to diverse plant species that are found in areas with alkaline conditions.
Highlights
For all plants, iron is an essential element for photosynthesis, DNA synthesis, and many other cellular functions
We focused on Petunia hybrida, which is a plant that use Strategy I, and established transformants by introducing the HvYS1 transporter gene and the PS, deoxymugineic acid (DMA), by which the plant acquired tolerance to iron deficiencies under alkali conditions
The leaves of the transgenic petunia were mashed, and the total RNA was extracted with an RNeasy Plant Mini Kit (QIAGEN GmbH, Hilden, Germany). cDNA was prepared from 1 μg of extracted RNA with a First Strand cDNA Synthesis Kit with the SuperScriptTM II RT enzyme (Life Technologies Corporation)
Summary
Iron is an essential element for photosynthesis, DNA synthesis, and many other cellular functions. Dicotyledonous plants use Strategy I to transport ferrous iron, Fe(II), from soil into the root cells through the iron-regulated transporter 1 (IRT1) after reduction from ferric iron, Fe(III), to Fe(II) by the ferric-chelate reductase FRO2 near the plasma membrane [7,8,9]. Graminaceous plants have a unique iron uptake system [10, 11], called Strategy II which is characterized by the synthesis [3, 12,13,14,15] of iron-chelating substances, phytosiderophores (PS), which are called mugineic acids (MAs) and which have molecular weights of about 300 and contain six functional groups for iron chelation [16, 17]. Further investigations have demonstrated that ZmYS1 is a proton/Fe (III)-PS cotransporter [20] that belongs to the oligopeptide transporter family, which is in doi:10.1371/journal.pone.0120227.g001
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