Undergraduate Research Scholar Dartmouth College Hanover, New Hampshire
Body of Abstract: Iron is one of the most vital micronutrients for plant life, as iron-containing enzymes are necessary for photosynthesis and cellular respiration. In plants, iron levels are finely regulated, with signaling pathways governing how iron is taken up, transported, and stored. Understanding how plants regulate iron could yield direct benefits for humanity — one-third of soils worldwide are iron-poor, while the majority of people rely on plants for dietary iron. Like other dicotyledonous plants, the model organism Arabidopsis thaliana employs a network of transcription factors to expresses the iron-transporter IRT1 and the iron-reductase FRO2 under iron deficiency. Here, we present data that the activation of the iron deficiency response occurs only in the light. Specifically, we have shown that red light signaling through several phytochromes, including Phytochrome B, is necessary for the activation of the iron deficiency response. Luciferase constructs driven by the promoter of various iron-regulated genes, including IRT1 and FRO2, showed activity only under red and white light, but not under blue light or in darkness. Similarly, plants exposed to red or white light showed detectable accumulation of the iron transporter protein IRT1 and induction of ferric-chelate reductase activity when grown under iron deficiency, in contrast to blue or dark-treated plants. RT-qPCR analysis revealed reduced expression of IRT1 and FRO2 transcripts in phyB and higher order phytochrome mutants; the phyB mutant showed reduced accumulation of IRT1 protein and greater sensitivity to leaf chlorosis under -Fe. Together, these findings demonstrate that red light sensed via phytochromes is necessary to activate the iron deficiency response. These findings may ultimately allow for the engineering of plants which constitutively take up iron regardless of light exposure and contribute to growing of iron-rich crops in artificial light conditions.