Development of a mugineic acid family phytosiderophore analog as an iron fertilizer

Iron (Fe) is an essential nutrient, but is poorly bioavailable because of its low solubility in alkaline soils; this leads to reduced agricultural productivity. To overcome this problem, we first showed that the soil application of synthetic 2′-deoxymugineic acid, a natural phytosiderophore from the Poaceae, can recover Fe deficiency in rice grown in calcareous soil. However, the high cost and poor stability of synthetic 2′-deoxymugineic acid preclude its agricultural use. In this work, we develop a more stable and less expensive analog, proline-2′-deoxymugineic acid, and demonstrate its practical synthesis and transport of its Fe-chelated form across the plasma membrane by Fe(III)•2’-deoxymugineic acid transporters. Possibility of its use as an iron fertilizer on alkaline soils is supported by promotion of rice growth in a calcareous soil by soil application of metal free proline-2’-deoxymugineic acid

Physiological and transcriptomic analysis of responses to different levels of iron excess stress in various rice tissues

<p>Iron (Fe) toxicity is a major nutritional disorder of plants and affects rice yield and production in rainfed and irrigated lowland rice grown in acid soils. Rice plants are reported to have exclusion and inclusion adaptation strategies for preventing damage from excess Fe. However, the molecular mechanisms behind the Fe toxicity response and the identities of the genes involved remain largely unknown. To reveal these mechanisms, we exposed rice plants to different levels of ferrous (Fe²⁺) excess treatment for 14 days and analyzed their growth, bronzing score, and mineral concentrations. Then, gene expression patterns in various tissues (roots, discrimination center [DC], stems, old leaves [OLs], and newest leaves [NLs]) in response to different levels of Fe excess (×1, ×10, ×20, ×50, and ×70 Fe) were examined using microarray analysis. Our results showed that the higher levels of Fe excess led to more Fe being preferentially translocated to OLs, thus avoiding Fe excess damage in the NL. We proposed three zones of Fe excess levels: the non-affected, affected, and dead zones. As an exclusion strategy, Fe uptake- and transport-related genes were suppressed in roots since in the non-affected zone. Roots are important for preventing Fe uptake to the plant body under Fe excess stress. As inclusion strategies, first, some genes highly induced in various tissues under Fe excess, such as <i>OsNAS3, OsVIT2</i>, and rice ferritin genes (<i>OsFers</i>), may be important for detoxification or isolation of excess Fe within the plant body. <i>OsZIPs</i> may contribute to the maintenance of zinc homeostasis. Second, the plant induces the expression of oxygen and electron transfer genes, cytochrome P450 family proteins, or some NAC-type transcription factors to avoid reactive oxygen species and abiotic stress caused by Fe excess in the affected zone. The plant may use similar Fe homeostasis mechanisms in the non-affected and affected zones in the NL and roots but employ different mechanisms in the OL, DC, and stem tissues. Our results will contribute to current screening and breeding efforts, which aim to develop Fe excess tolerance in diverse rice cultivars, thus increasing rice production in lowland fields.</p

Analysis of the spatial expression patterns of rice iron deficiency-responsive element-binding factors IDEF1 and IDEF2

Iron (Fe) is critical for plant growth. Under conditions of low Fe availability, rice plants induce genes involved in Fe uptake and utilization. Recently, we identified the iron-deficiency-responsive cis-acting elements IDE1 and IDE2, which are bound in a specific manner by IDE-binding factors 1 and 2 (IDEF1 and IDEF2, respectively). IDEF1 and IDEF2 regulate genes related to the Fe-deficiency response. In the present study, we examined the spatial expression patterns of IDEF1 and IDEF2 during the germination, vegetative, and seed-maturation stages by assessing their localization in IDEF1 and IDEF2 promoter–GUS transgenic rice lines. During germination, IDEF1 and IDEF2 were expressed in the endosperm and embryo. In hydroponic culture experiments, the expression patterns of IDEF1 and IDEF2 were similar under both Fe-deficient and Fe-sufficient conditions during the vegetative stage. In leaves, IDEF1 expression was observed in mesophyll cells and in small vascular bundles, whereas IDEF2 was highly expressed in vascular bundles. In root sections, IDEF1 and IDEF2 were highly expressed in secondary roots and inside vascular bundles. IDEF1 was also expressed in pollen from flowers before and after anthesis, in the ovary after fertilization, and in the embryo during seed maturation. IDEF2 was expressed in flowering stage pollen, in immature seeds just after flowering, and in the dorsal vascular region during the late maturation stage. The spatial expression patterns of IDEF1 and IDEF2 partially overlapped with their target genes

Iron biofortification of Myanmar rice

Iron (Fe) deficiency causes elevates human mortality rates, especially in developing countries. In Myanmar, the prevalence of Fe-deficient anemia in children and pregnant women are 75% and 71%, respectively. Myanmar people have one of the highest per capita rice consumption rates globally. Consequently, production of Fe-biofortified rice would likely contribute to solving the Fe-deficiency problem in this human population. To produce Fe-biofortified Myanmar rice by transgenic methods, we first analyzed callus induction and regeneration efficiencies in 15 varieties that are presently popular because of their high yields and/or qualities. Callus formation and regeneration efficiency in each variety was strongly influenced by types of culture media containing a range of 2,4-dichlorophenoxyacetic acid concentrations. The Paw San Yin variety, which has a high Fe content in polished seeds, performed well in callus induction and regeneration trials. Thus, we transformed this variety using a gene expression cassette that enhanced Fe transport within rice plants through overexpression of the nicotianamine synthase gene HvNAS1, Fe flow to the endosperm through the Fe(II)-nicotianamine transporter gene OsYSL2, and Fe accumulation in endosperm by the Fe storage protein gene SoyferH2. A line with a transgene insertion was successfully obtained. Enhanced expressions of the introduced genes OsYSL2, HvNAS1, and SoyferH2 occurred in immature T2 seeds. The transformants accumulated 3.4-fold higher Fe concentrations, and also 1.3-fold higher zinc concentrations in T2 polished seeds compared to levels in non-transgenic rice. This Fe-biofortified rice has the potential to reduce Fe-deficiency anemia in millions of Myanmar people without changing food habits and without introducing additional costs