Abstract
Abstract Iron deficiency is a major cause of reduced crop yields worldwide, particularly in calcareous soils. Unlike barley, rice is highly susceptible to iron deficiency because of a low capacity to secrete mugineic acid family phytosiderophores (MAs), which are iron chelators secreted by graminaceous plants. We present an approach toward the generation along with field trials of transgenic rice lines exhibiting increased tolerance to iron deficiency. Cloning barley genes that encode biosynthetic enzymes for MAs enabled us to produce transgenic rice plants by introducing barley MAs biosynthesis-related genes. We tested three transgenic lines possessing barley genomic fragments responsible for MAs biosynthesis in a paddy field experiment on calcareous soil, which revealed tolerance of these lines to low iron availability. We also applied new approaches to generate iron-deficiency-tolerant rice lines, including the introduction of an engineered ferric-chelate reductase gene and manipulation of transcription factor genes regulating the iron deficiency response.
Highlights
Introduction of barley genes responsible formugineic acid family phytosiderophores (MAs) biosynthesis into rice To produce transgenic rice plants with enhanced tolerance to Fe deficiency by increasing MAs production capacity, we introduced barley HvNAS1, HvNAAT-A, HvNAAT-B, and/or IDS3 genes using either their genomic fragments or the IDS3 gene promoter to confer inducibility to Fe deficiency
The strategy II mechanism, which is specific to graminaceous plants, is mediated by natural Fe chelators, the mugineic acid family phytosiderophores (MAs)
Introduction of barley genes responsible for MAs biosynthesis into rice To produce transgenic rice plants with enhanced tolerance to Fe deficiency by increasing MAs production capacity, we introduced barley HvNAS1, HvNAAT-A, HvNAAT-B, and/or IDS3 genes using either their genomic fragments or the IDS3 gene promoter to confer inducibility to Fe deficiency
Summary
Iron (Fe) is essential for most living organisms including plants. abundant in mineral soils, Fe is sparingly soluble under aerobic conditions at high soil pH, especially in calcareous soils, which account for about 30% of the world’s cultivated soils. The strategy I mechanism, utilized by nongraminaceous plants, includes induction of ferric-chelate reductase to reduce Fe at the root surface to the more soluble ferrous form and transport the ferrous ions generated across the root plasma membrane. The strategy II mechanism, which is specific to graminaceous plants, is mediated by natural Fe chelators, the mugineic acid family phytosiderophores (MAs). Barley secretes large amounts of MAs, including mugineic acid (MA), 3-epihydroxy-2’-deoxymugineic acid (epiHDMA), and 3-epihydroxymugineic acid (epiHMA), in addition to DMA, under Fe deficiency; it is more. We hypothesized that introducing barley genes responsible for MAs biosynthesis into rice would lead to enhanced MAs production and tolerance in calcareous soils. We successfully produced various transgenic rice lines showing enhanced tolerance to low Fe availability by introducing barley MAs biosynthesis genes. Future perspectives on generating further favorable and commonly acceptable transformants are described
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