Long distance signaling of iron deficiency via phloem

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

This project aims to discover novel mechanisms that control the uptake and distribution of iron in plants. Part of the impetus for such discovery research is that iron deficiency is one of the most significant micronutrient malnutrition problems facing the world today. The World Health Organization estimates that ~1.62 billion people--~25% of the world's population-- are affected by iron deficiency. The production of staple crops that have elevated iron in edible parts (e.g., in the grains of cereals) is widely regarded as the primary means by which this problem could be stably addressed. However, this goal is thwarted because our knowledge of the molecular mechanisms controlling iron accumulation in plants is far from complete. The scientists conducting this project have discovered that three distinct iron transporter proteins are required in the leaves of plants 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 the leaf transporters will reveal new mechanisms that plants use to control iron uptake. In addition to these scientific goals, the researchers will work to enhance educational opportunities for undergraduates and K-12 students through the development of multimedia web modules for K-12 outreach, and the development of course based undergraduate 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 in controlling shoot-to-root signaling of iron status. A working hypothesis that explains current observations is that OPT3 and YSL1/YSL3 together modulate phloem companion cell Fe status, and that low concentrations of Fe in the companion cells results in the production of a phloem mobile signal that initiates iron deficiency regulated gene expression in roots. In this project, a combination of transporter activity studies, protein localization, and highly accurate determination of the metal distribution in veins will test this hypothesis. The project scientists have established the presence of a phloem-mobile inductive RNA signal that is capable of inducing iron deficiency associated gene expression in excised roots. Because a simple assay system for the phloem mobile signal has been developed, profiling experiments coupled with downstream genetic analyses will be used to identify the phloem mobile signal produced in iron deficient leaves 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.