title: A new transgenic rice line exhibiting enhanced ferric iron reduction and phytosiderophore production confers tolerance to low iron availability in calcareous soil.
abstract: Iron (Fe) deficiency is a critical agricultural problem, especially in calcareous soil, which is distributed worldwide. Rice plants take up Fe(II) from soil through a OsIRT1 transporter (Strategy I-related system) and also take up Fe(III) via a phytosiderophore-based system (Strategy II system). However, rice plants are susceptible to low-Fe conditions because they have low Fe(III) reduction activity and low-level phytosiderophore secretion. Previously, we produced transgenic rice plants expressing a mutationally reconstructed yeast ferric chelate reductase, refre1/372, under the control of the OsIRT1 promoter. This transgenic rice line exhibited higher Fe(III) chelate reductase activity and tolerance to Fe deficiency. In addition, we produced transgenic rice overexpressing the Fe deficiency-inducible transcription factor, OsIRO2, which regulates the expression of various genes involved in the strategy II Fe(III) uptake system, including OsNAS1, OsNAAT1, OsDMAS1, OsYSL15, and TOM1. This transgenic rice exhibited improved phytosiderophore secretion ability and tolerance to Fe deficiency. In the present research, transgenic rice plants that possess both the OsIRT1 promoter-refre1/372 and the 35S promoter-OsIRO2 (RI lines) were produced to enhance both Strategy I Fe(II) reductase ability and Strategy II phytosiderophore productivity. RI lines exhibited enhanced tolerance to Fe-deficient conditions at the early and middle-late stages of growth in calcareous soil, compared to both the non-transgenic line and lines harboring either OsIRT1 promoter-refre1/372 or 35S promoter-OsIRO2 alone. RI lines also exhibited a 9-fold higher yield than the non-transgenic line. Moreover, we successfully produced Fe-deficiency-tolerant Tachisugata rice, which is a high-biomass variety used as fodder. Collectively, our results demonstrate that combined enhancement of two Fe uptake systems in rice is highly effective in conferring tolerance to low Fe availability in calcareous soil.
authors.affiliation: Research Institute for Bioresources and Biotechnology, Ishikawa Prefectural University, Nonoichi, Ishikawa, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Masuda
authors.affiliation: Research Institute for Bioresources and Biotechnology, Ishikawa Prefectural University, Nonoichi, Ishikawa, Japan.
authors.forename: Erika
authors.initials: E
authors.lastname: Shimochi
authors.affiliation: Research Institute for Bioresources and Biotechnology, Ishikawa Prefectural University, Nonoichi, Ishikawa, Japan.
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Hamada
authors.affiliation: Research Institute for Bioresources and Biotechnology, Ishikawa Prefectural University, Nonoichi, Ishikawa, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Senoura
authors.affiliation: Research Institute for Bioresources and Biotechnology, Ishikawa Prefectural University, Nonoichi, Ishikawa, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: Research Institute for Bioresources and Biotechnology, Ishikawa Prefectural University, Nonoichi, Ishikawa, Japan.
authors.forename: May Sann
authors.initials: MS
authors.lastname: Aung
authors.affiliation: Graduate School of Science, Tohoku University, Aoba, Sendai, Miyagi, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Ishimaru
authors.affiliation: Functional Plant Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ogo
authors.affiliation: Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Nakanishi
authors.affiliation: Research Institute for Bioresources and Biotechnology, Ishikawa Prefectural University, Nonoichi, Ishikawa, Japan.
authors.forename: Naoko K
authors.initials: NK
authors.lastname: Nishizawa
mesh_terms: D018533:Biomass; D002119:Calcium Carbonate / Q000032:analysis*; D038181:FMN Reductase / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D012275:Oryza / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D010084:Oxidation-Reduction; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic / Q000235:genetics; D017262:Siderophores / Q000378:metabolism*; D012987:Soil / Q000737:chemistry*
chemical_list: D026901:Membrane Transport Proteins; D017262:Siderophores; D012987:Soil; D007501:Iron; D038181:FMN Reductase; C023903:ferric citrate iron reductase; D002119:Calcium Carbonate