Integrating Signals in Iron Homeostasis

Iron often limits plant growth and agricultural yield. Furthermore, more than 2 billion people are iron deficient because their plant-based diets are not a rich source of iron, making iron deficiency the most prevalent nutritional problem in the world today. Clearly, understanding iron metabolism in plants is crucial, both from the point of view of improving plant growth and crop yields, as well as improving human nutrition.

Despite progress in tracing how iron moves throughout the plant, scientists still do not understand how plants integrate information about iron supply and light conditions. This project will help to explain how a protein called URI receives and then conveys information about both the iron status of a cell and light quality. In partnership with the New Hampshire Academy of Science, students in grades 6-12 will be offered research experiences that will raise their appreciation for all that plants do and teach them how to leverage the power of plants to ensure long term sustainability and health.

NHAS runs summer and after school discovery-based scientific research programs for students from a wide geographic section of NH and VT. Their outreach covers rural areas where students generally have few opportunities to experience authentic scientific research. Broader impacts will also include training the next generation of scientists. Undergraduates from several different mentoring programs will participate in the proposed work.

Iron is an essential nutrient for plants, yet too much iron can be toxic. Therefore, plants only take up iron when needed. The essential bHLH transcription factor, URI/bHLH121, is required for mounting the iron deficiency response.

A phosphorylated form of URI accumulates under iron deficiency, forms heterodimers with subgroup bHLH IVc transcription factors and induces transcription of another class of transcription factors, the sub-group Ib bHLH. These Ib bHLH in turn heterodimerize with FIT/bHLH29, and drive the transcription of the genes encoding the iron transporter IRT1 and the ferric chelate reductase FRO2, to increase iron uptake.

Although the mechanisms controlling iron uptake from the soil are now relatively well understood, little is known about how URI may integrate information about iron supply and light conditions. Light is required for URI phosphorylation, suggesting that a light-regulated kinase is involved. Genetic experiments were designed to determine whether URI phosphorylation is a red light or blue light response, and whether members of the photoregulatory kinase (PPK) family are involved.

Experiments will also address a second point in the iron deficiency pathway where light information is required, namely the induction of the FIT transcription factor. The long-term goal is to understand the entire network of genes responsible for orchestrating a coordinated response to iron deficiency at the whole plant level. Such an understanding will transform efforts towards sustainable improvements of crop yields, in terms of plant productivity and nutrient content.

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.