Table_3_B3 Transcription Factors Determine Iron Distribution and FERRITIN Gene Expression in Embryo but Do Not Control Total Seed Iron Content.xlsx

Iron is an essential micronutrient for humans and other organisms. Its deficiency is one of the leading causes of anemia worldwide. The world health organization has proposed that an alternative to increasing iron content in food is through crop biofortification. One of the most consumed part of crops is the seed, however, little is known about how iron accumulation in seed occurs and how it is regulated. B3 transcription factors play a critical role in the accumulation of storage compounds such as proteins and lipids. Their role in seed maturation has been well characterized. However, their relevance in accumulation and distribution of micronutrients like iron remains unknown. In Arabidopsis thaliana and other plant models, three master regulators belonging to the B3 transcription factors family have been identified: FUSCA3 (FUS3), LEAFY COTYLEDON2 (LEC2), and ABSCISIC ACID INSENSITIVE 3 (ABI3). In this work, we studied how seed iron homeostasis is affected in B3 transcription factors mutants using histological and molecular approaches. We determined that iron distribution is modified in abi3, lec2, and fus3 embryo mutants. For abi3-6 and fus3-3 mutant embryos, iron was less accumulated in vacuoles of cells surrounding provasculature compared with wild type embryos. lec2-1 embryos showed no difference in the pattern of iron distribution in hypocotyl, but a dramatic decrease of iron was observed in cotyledons. Interestingly, for the three mutant genotypes, total iron content in dry mutant seeds showed no difference compared to wild type. At the molecular level, we showed that genes encoding the iron storage ferritins proteins are misregulated in mutant seeds. Altogether our results support a role of the B3 transcription factors ABI3, LEC2, and FUS3 in maintaining iron homeostasis in Arabidopsis embryos.

铁是人类及其他生物体必需的微量营养素（micronutrient），其缺乏是全球范围内贫血的主要致病因素之一。世界卫生组织（World Health Organization）提出，通过作物生物强化（crop biofortification）是提升食物中铁含量的替代方案。作物中最常被食用的部分之一是种子，但目前人们对种子中铁的积累过程及其调控机制仍知之甚少。B3转录因子（B3 transcription factors）在蛋白质、脂质等贮藏化合物的积累过程中发挥关键作用，其在种子成熟过程中的功能已得到充分阐释。然而，它们在铁等微量营养素的积累与分布中的作用仍不明确。在拟南芥（Arabidopsis thaliana）及其他植物模式物种中，已鉴定出隶属于B3转录因子家族的3个核心调控因子：FUSCA3（FUS3）、LEAFY COTYLEDON2（LEC2）以及ABSCISIC ACID INSENSITIVE 3（ABI3）。本研究通过组织学与分子生物学手段，探究了B3转录因子突变体中种子铁稳态（iron homeostasis）的变化情况。研究发现，abi3、lec2及fus3胚胎突变体的铁分布模式发生了改变。与野生型胚胎相比，abi3-6与fus3-3突变体胚胎的原维管（provasculature）周围细胞液泡中铁的积累量更低。lec2-1突变体胚胎的下胚轴（hypocotyl）铁分布模式未出现明显差异，但子叶（cotyledon）中的铁含量出现显著下降。值得注意的是，相较于野生型种子，三种突变体的干燥种子总铁含量未出现显著差异。在分子层面，本研究发现突变体种子中编码铁贮藏蛋白铁蛋白（ferritin）的基因表达失调。综上，本研究结果证实，B3转录因子ABI3、LEC2及FUS3在维持拟南芥胚胎铁稳态中发挥重要作用。