MYB10 and MYB72 Are Required for Growth under Iron-Limiting Conditions

Iron is essential for photosynthesis and is often a limiting nutrient for plant productivity. Plants respond to conditions of iron deficiency by increasing transcript abundance of key genes involved in iron homeostasis, but only a few regulators of these genes have been identified. Using genome-wide expression analysis, we searched for transcription factors that are induced within 24 hours after transferring plants to iron-deficient growth conditions. Out of nearly 100 transcription factors shown to be up-regulated, we identified MYB10 and MYB72 as the most highly induced transcription factors. Here, we show that MYB10 and MYB72 are functionally redundant and are required for plant survival in alkaline soil where iron availability is greatly restricted. myb10myb72 double mutants fail to induce transcript accumulation of the nicotianamine synthase gene NAS4. Both myb10myb72 mutants and nas4-1 mutants have reduced iron concentrations, chlorophyll levels, and shoot mass under iron-limiting conditions, indicating that these genes are essential for proper plant growth. The double myb10myb72 mutant also showed nickel and zinc sensitivity, similar to the nas4 mutant. Ectopic expression of NAS4 rescues myb10myb72 plants, suggesting that loss of NAS4 is the primary defect in these plants and emphasizes the importance of nicotianamine, an iron chelator, in iron homeostasis. Overall, our results provide evidence that MYB10 and MYB72 act early in the iron-deficiency regulatory cascade to drive gene expression of NAS4 and are essential for plant survival under iron deficiency.

铁是光合作用所必需的元素，同时往往也是限制植物生产力的限制性营养因子。植物会通过提升铁稳态相关关键基因的转录本丰度来响应缺铁环境，但目前仅鉴定出少数这类基因的调控因子。本研究通过全基因组表达分析，筛选了将植物转移至缺铁生长条件后24小时内被诱导表达的转录因子。在近100个被证实上调表达的转录因子中，我们鉴定出MYB10与MYB72为上调幅度最高的转录因子。本研究证实，MYB10与MYB72存在功能冗余，且是植物在铁有效性大幅受限的碱性土壤中存活所必需的。myb10myb72双突变体无法诱导烟酰胺合酶基因NAS4的转录本积累。在缺铁条件下，myb10myb72双突变体与nas4-1突变体均表现出铁浓度、叶绿素水平及地上部生物量降低的表型，表明这些基因对植物正常生长至关重要。myb10myb72双突变体亦表现出与nas4突变体类似的镍、锌敏感性缺陷。异位表达NAS4可挽救myb10myb72突变体的表型，提示NAS4功能缺失是该类突变体的核心缺陷，同时凸显了作为铁螯合剂的烟酰胺在铁稳态中的重要性。综上，本研究结果表明，MYB10与MYB72在缺铁调控级联反应中发挥早期作用，驱动NAS4的基因表达，且对于植物在缺铁环境下的存活不可或缺。