Abstract Soils of large areas of the globe are affected by deficiency or toxicity of iron (Fe), making it one of the major limitations to higher productivity of rice. Deficiency of Fe, an essential micronutrient for growth and development of rice, produces grain with low Fe-content. Consumption of low-Fe rice causes malnutrition affecting human health. Biofortification is an easy and low-cost way to enhance Fe content in rice, the staple food of more than half of the global population. Identification of relevant quantitative trait loci (QTLs) and genes controlling the stresses are needed for developing tolerant genotype(s). Fe deficiency is commonly observed in alkaline and aerobic soils, while toxicity is seen in low pH soils of lowland rice ecology. Rice plants cope up under deficiency or toxicity conditions through various morphological, physiological and differential gene expression strategies. Rice plant uses various transporter genes like OsNAS1, OsNAS2, OsIRT1, OsIRT2, OsNRAMP1, OsYSL15 and OsYSL16 under deficiency stress while OsIRT1, OsFRO2, OsVIT1, OsVIT2, OsNRAMP6, OsNAAT1, OsNAS3, OsNAC4, OsNAC5 and OsNAC6 under toxicity condition are involved for Fe homeostasis. Several QTLs including qFe3:1, qFe3:2, qFe7:1, qFe9:1, qFe9:2, qFe10:1, Fe11:1, qFe3.3 and qFe7.3 associated with grain-Fe content have been identified. Many Fe binding and transporters genes like OsZIP1, OsHMA4, OsACA2, OsZIP2, OsCNGC, OsZIP3, OsZIP5, OsZIP9, OsHma2, ABC transporter, OsNAS3, heavy metal transporter, Chy zinc finger and OsACA9 have been identified to improve grain-Fe content. Donor lines for grain-Fe content have been identified from rice germplasms showing even up to 147 μg g−1 in brown rice. Fe content in rice grain has been enhanced to many folds using ferritin genes of soybean and common bean, NAS gene and mugineic acid synthase genes (HvNAS1 and HvNAAT-A,-B or IDS3) of barley, nicotianamine transporter gene (OsYSL2) and nicotinamine synthase genes (OsNAS1, OsNAS2 and OsNAS3) through transgenic approach. The paper analyses the mechanisms of tolerance to Fe-deficiency and toxicity, identification of genes/QTLs responsible for tolerance under the stresses and helping for biofortification, assesses the stress affected symptoms, reviews the screening and summarizes the efforts for breeding programs for improving tolerance to Fe-deficiency and toxicity in rice.

中文翻译：

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水稻中铁稳态、吸收、生物强化和增效的遗传调控

摘要 全球大部分地区的土壤都受到铁（Fe）缺乏或毒性的影响，使其成为提高水稻生产力的主要限制因素之一。铁是水稻生长发育的必需微量营养素，缺乏铁会导致谷物中铁含量低。食用低铁大米会导致营养不良，影响人类健康。生物强化是一种提高大米中铁含量的简单且低成本的方法，大米是全球一半以上人口的主食。开发耐受基因型需要相关数量性状基因座 (QTL) 和控制胁迫的基因的鉴定。在碱性和好氧土壤中通常观察到缺铁，而在低地水稻生态的低 pH 土壤中观察到毒性。水稻植物通过各种形态、生理和差异基因表达策略。水稻在缺乏胁迫下使用各种转运蛋白基因，如 OsNAS1、OsNAS2、OsIRT1、OsIRT2、OsNRAMP1、OsYSL15 和 OsYSL16，而 OsIRT1、OsFRO2、OsVIT1、OsVIT2、OsNRAMP6、OsNAAT1、OsNAS4、OsNACNA 条件下的 OsNAC5体内平衡。已经确定了几个与晶粒-Fe 含量相关的 QTL，包括 qFe3:1、qFe3:2、qFe7:1、qFe9:1、qFe9:2、qFe10:1、Fe11:1、qFe3.3 和 qFe7.3。许多 Fe 结合和转运基因，如 OsZIP1、OsHMA4、OsACA2、OsZIP2、OsCNGC、OsZIP3、OsZIP5、OsZIP9、OsHma2、ABC 转运蛋白、OsNAS3、重金属转运蛋白、Chy 锌指和 OsACA9 已被鉴定可提高谷物铁含量。已从水稻种质中鉴定出谷物铁含量的供体系，糙米中甚至高达 147 μg g-1。使用大豆和普通豆的铁蛋白基因、NAS 基因和大麦的麦根酸合酶基因（HvNAS1 和 HvNAAT-A、-B 或 IDS3）、烟胺转运蛋白基因 (OsYSL2) 和烟胺，水稻籽粒中的铁含量已提高了许多倍通过转基因方法合成酶基因（OsNAS1、OsNAS2 和 OsNAS3）。该论文分析了对缺铁和毒性的耐受机制，鉴定了负责胁迫下耐受和帮助生物强化的基因/QTL，评估了胁迫影响的症状，审查了筛选并总结了提高对铁缺乏耐受性的育种计划的努力。水稻缺铁与毒性. -B 或 IDS3) 的大麦、烟胺转运蛋白基因 (OsYSL2) 和烟胺合酶基因 (OsNAS1、OsNAS2 和 OsNAS3) 通过转基因方法。该论文分析了对缺铁和毒性的耐受机制，鉴定了负责胁迫下耐受和帮助生物强化的基因/QTL，评估了胁迫影响的症状，审查了筛选并总结了提高对铁缺乏耐受性的育种计划的努力。水稻缺铁与毒性. -B 或 IDS3) 的大麦、烟胺转运蛋白基因 (OsYSL2) 和烟胺合酶基因 (OsNAS1、OsNAS2 和 OsNAS3) 通过转基因方法。该论文分析了对缺铁和毒性的耐受机制，鉴定了负责胁迫下耐受和帮助生物强化的基因/QTL，评估了胁迫影响的症状，审查了筛选并总结了提高对铁缺乏耐受性的育种计划的努力。水稻缺铁与毒性.