Long distance signaling of iron deficiency via phloem

该项目旨在发现控制铁在植物中的吸收和分布的新机制。推动这类发现研究的部分原因是，缺铁是当今世界面临的最严重的微量营养素营养不良问题之一。世界卫生组织估计，约16.2亿人——约占世界人口的25%——患有缺铁症。人们普遍认为，生产可食用部分（如谷物）铁含量较高的主粮作物是稳定解决这一问题的主要手段。然而，由于我们对控制植物铁积累的分子机制的了解远未完成，这一目标受到了阻碍。进行这项研究的科学家们发现，植物的叶片需要三种不同的铁转运蛋白，才能将缺铁的正确信号传递给根部。由于根系根据叶片的信号吸收铁，对叶片转运蛋白的研究将揭示植物控制铁吸收的新机制。除了这些科学目标之外，研究人员还将通过开发用于K-12扩展的多媒体网络模块和开发基于课程的本科生研究经验（CURES），努力提高本科生和K-12学生的教育机会。先前对拟南芥铁转运蛋白OPT3、YSL1和YSL3的调控和定位研究表明，它们在控制铁状态的茎到根信号传导中具有相反但不可或缺的作用。一种解释当前观察结果的假说是，OPT3和YSL1/YSL3共同调节韧皮部伴细胞的铁状态，而伴细胞中低浓度的铁会导致韧皮部移动信号的产生，从而引发根中铁缺乏的基因表达。在这个项目中，转运蛋白活性研究、蛋白质定位和高度精确的金属在静脉分布的测定相结合将验证这一假设。该项目的科学家已经确定了韧皮部移动诱导RNA信号的存在，该信号能够在切除的根中诱导铁缺乏相关的基因表达。由于已经开发了一个简单的韧皮部移动信号分析系统，分析实验结合下游遗传分析将用于鉴定缺铁叶片中产生的调节根基因表达的韧皮部移动信号。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project aims to discover novel mechanisms that control the uptake and distributionof iron in plants. Part of the impetus for such discovery research is that iron deficiencyis one of the most significant micronutrient malnutrition problems facing the worldtoday. The World Health Organization estimates that ~1.62 billion people--~25% of theworld's population-- are affected by iron deficiency. The production of staple crops thathave elevated iron in edible parts (e.g., in the grains of cereals) is widely regarded as theprimary means by which this problem could be stably addressed. However, this goal isthwarted because our knowledge of the molecular mechanisms controlling ironaccumulation in plants is far from complete. The scientists conducting this project havediscovered that three distinct iron transporter proteins are required in the leaves ofplants in order for those leaves to send correct signals of iron deficiency to the roots.Since the roots take up iron in response to signals from the leaves, investigation of theleaf transporters will reveal new mechanisms that plants use to control iron uptake. Inaddition to these scientific goals, the researchers will work to enhance educationalopportunities for undergraduates and K-12 students through the development of multimediaweb modules for K-12 outreach, and the development of course basedundergraduate research experiences (CURES).Prior work on the regulation and localization of Arabidopsis iron transporters, OPT3,YSL1 and YSL3 has indicated that they have opposite but indispensable roles incontrolling shoot-to-root signaling of iron status. A working hypothesis that explainscurrent observations is that OPT3 and YSL1/YSL3 together modulate phloem companioncell Fe status, and that low concentrations of Fe in the companion cells results in theproduction of a phloem mobile signal that initiates iron deficiency regulated geneexpression in roots. In this project, a combination of transporter activity studies, proteinlocalization, and highly accurate determination of the metal distribution in veins will testthis hypothesis. The project scientists have established the presence of a phloem-mobileinductive RNA signal that is capable of inducing iron deficiency associated geneexpression in excised roots. Because a simple assay system for the phloem mobilesignal has been developed, profiling experiments coupled with downstream geneticanalyses will be used to identify the phloem mobile signal produced in iron deficientleaves that regulates root gene expression.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.