Iron (Fe) is an essential micronutrient whose availability is limiting in many soils. During Fe deficiency, plants alter the expression of many genes to increase Fe uptake, distribution, and utilization. In a genetic screen for suppressors of Fe sensitivity in the E3 ligase mutant bts-3, we isolated an allele of the bHLH transcription factor (TF) ILR3, ilr3-4. We identified a striking leaf bleaching phenotype in ilr3 mutants that was suppressed by limiting light intensity, indicating that ILR3 is required for phototolerance during Fe deficiency. Among its paralogs that are thought to be partially redundant, only ILR3 was required for phototolerance as well as repression of genes under Fe deficiency. A mutation in the gene-encoding PYE, a known transcriptional repressor under Fe deficiency, also caused leaf bleaching. We identified singlet oxygen as the accumulating reactive oxygen species (ROS) in ilr3-4 and pye, suggesting photosensitivity is due to a PSII defect resulting in ROS production. During Fe deficiency, ilr3-4 and pye chloroplasts retain normal ultrastructure and, unlike wild type (WT), contain stacked grana similar to Fe-sufficient plants. Additionally, we found that the D1 subunit of PSII is destabilized in WT during Fe deficiency but not in ilr3-4 and pye, suggesting that PSII repair is accelerated during Fe deficiency in an ILR3- and PYE-dependent manner. Collectively, our results indicate that ILR3 and PYE confer photoprotection during Fe deficiency to prevent the accumulation of singlet oxygen, potentially by promoting reduction of grana stacking to limit excitation and facilitate repair of the photosynthetic machinery.

铁 (Fe) 是一种必需的微量营养素，在许多土壤中其可用性受到限制。在缺铁期间，植物会改变许多基因的表达以增加铁的吸收、分布和利用。在 E3 连接酶突变体bts-3中 Fe 敏感性抑制因子的遗传筛选中，我们分离了 bHLH 转录因子 (TF) ILR3的等位基因，ilr3-4。我们在ilr3突变体中发现了一种引人注目的叶片漂白表型，该表型被限制光强度抑制，表明 ILR3 是缺铁期间耐光性所必需的。在其被认为部分冗余的旁系同源物中，只有ILR3是耐光性以及在缺铁下抑制基因所必需的。编码 PYE 的基因（一种已知的缺铁条件下的转录抑制因子）的突变也导致叶片白化。我们将单线态氧鉴定为ilr3-4和pye中积累的活性氧 (ROS) ，这表明光敏性是由于 PSII 缺陷导致 ROS 产生。在缺铁期间，ilr3-4和pye叶绿体保留正常的超微结构，并且与野生型 (WT) 不同，它们含有类似于铁充足植物的堆叠颗粒。此外，我们发现 PSII 的 D1 亚基在缺铁期间在 WT 中不稳定，但在ilr3-4和pye中没有，表明在缺铁期间，PSII 修复以 ILR3 和 PYE 依赖的方式加速。总的来说，我们的结果表明 ILR3 和 PYE 在缺铁期间提供光保护，以防止单线态氧的积累，可能通过促进颗粒堆积的减少来限制激发和促进光合机制的修复。