Meta-Analysis of Iron Excess Stress in Rice: Genes and Mechanisms of Tolerance to Acidic Soil

Iron toxicity, predominantly stemming from excessive levels of ferrous iron (Fe²⁺) in acidic soils, poses a considerable challenge for crop production. Hypoxic conditions induced by waterlogging can exacerbate Fe²⁺ availability, which significantly impacts the cultivation and productivity of rice (Oryza sativa), a staple food for millions worldwide. In several regions across South America, Africa, and Asia, the prevalence of acidic soils results in elevated Fe²⁺ levels leading to iron toxicity, thereby hindering rice yield. Some regional rice varieties demonstrate a notable adaptation to high iron conditions, offering insights into the tolerance mechanisms through comparative physiology and transcriptomic studies. This review synthesizes the various strategies employed by rice plants to mitigate iron toxicity stress, with a focus on the regulation of essential genes and genetic pathways associated with iron transport and homeostasis. We place particular emphasis on the co-expression networks and predicted subcellular localization of the proteins encoded by these genes. A meta-analysis of differential gene expression data gathered from studies involving six distinct rice lines-either tolerant or sensitive-reveals significant influences of plant genotype, developmental stage, and treatment type on the expression patterns, leading to the identification of robust marker genes associated with the iron excess response. Our comprehensive literature review uncovers several critical knowledge gaps, establishing a framework for developing novel approaches aimed at elucidating the molecular mechanisms underpinning iron stress tolerance. These insights are vital for enhancing rice yield in iron-rich, acidic soils, ultimately contributing to improved food security in affected regions.