Iron (Fe) is an essential nutrient for all living organisms but can lead to cytotoxicity when present in excess. Fe toxicity often occurs in rice grown in submerged paddy fields with low pH, leading dramatical increases in ferrous ion concentration, disrupting cell homeostasis and impairing growth and yield. However, the underlying molecular mechanisms of Fe toxicity response and tolerance in plants are not well characterized yet. Microarray and genome-wide association analyses have shown that rice employs four defense systems to regulate Fe homeostasis under Fe excess. In defense 1, Fe excess tolerance is implemented by Fe exclusion as a result of suppression of genes involved in Fe uptake and translocation such as OsIRT1, OsYSL2, OsTOM1, OsYSL15, OsNRAMP1, OsNAS1, OsNAS2, OsNAAT1, OsDMAS1, and OsIRO2. The Fe-binding ubiquitin ligase, HRZ, is a key regulator that represses Fe uptake genes in response to Fe excess in rice. In defense 2, rice retains Fe in the root system rather than transporting it to shoots. In defense 3, rice compartmentalizes Fe in the shoot. In defense 2 and 3, the vacuolar Fe transporter OsVIT2, Fe storage protein ferritin, and the nicotinamine synthase OsNAS3 mediate the isolation or detoxification of excess Fe. In defense 4, rice detoxifies the ROS produced within the plant body in response to excess Fe. Some OsWRKY transcription factors, S-nitrosoglutathione-reductase variants, p450-family proteins, and OsNAC4, 5, and 6 are implicated in defense 4. These knowledge will facilitate the breeding of tolerant crops with increased productivity in low-pH, Fe-excess soils.

铁（Fe）是所有活生物体必不可少的营养素，但过量存在会导致细胞毒性。Fe毒性通常发生在pH值较低的淹水稻田中，导致亚铁离子浓度急剧增加，破坏了细胞的稳态并损害了生长和产量。但是，Fe毒性反应和植物耐受性的潜在分子机制尚未得到很好的表征。基因芯片和全基因组关联分析表明，水稻在铁过量时采用四种防御系统调节铁稳态。在防御1中，通过抑制与铁摄取和转运有关的基因（例如OsIRT1， OsYSL2， OsTOM1， OsYSL15， OsNRAMP1， OsNAS1， OsNAS2， OsNAAT1， OsDMAS1和 OsIRO2。结合铁的泛素连接酶HRZ是一种关键调节剂，可响应水稻中的铁过量而抑制铁的摄取基因。在防御2中，水稻将Fe保留在根系中，而不是将其运输到芽中。在防御3中，大米将芽中的铁分隔。在防御2和3中，液泡铁转运蛋白OSVIT2，铁存储蛋白铁蛋白和烟碱合酶 OsNAS3介导过量铁的分离或解毒。在防御措施4中，大米可以消除铁体内过量的铁而产生的活性氧。一些奥斯威基 转录因子 S-亚硝基谷胱甘肽还原酶 变体，p450家族蛋白和 OsNAC4， 5和 6 与防御4有关。这些知识将有助于在低pH，铁过量的土壤中以高生产力促进耐性作物的育种。