Sensing and systemic signaling of iron homeostasis in plants – IRONSENS

Iron (Fe) is a limiting factor for crop yields and an important element in human diets. We (Taiwanese partner) have discovered two ways to enhance Fe accumulation in plants. The first one consists in increasing the expression of a family of peptides called IRONMAN (IMAs) involved in the signaling of the Fe status. This novel peptide family regulates Fe uptake by modulating the activity of specific E3-ubiquitin ligases which target for degradation via the 26S proteasome key bHLH transcription factors (TFs) involved in the regulation of Fe homeostasis. We have also identified a dominant mutation in a gene that encodes one of these TFs. This allele constitutively activates Fe uptake by roots, and leads to an accumulation of Fe in all parts of the plant. We (French partner) have identified key TFs which play a central role in the regulation of genes involved in the response to Fe excess and Fe deficiency, including IMA genes and genes encoding TFs regulated by IMAs. This negative feedback loop controls the perception and regulation of Fe homeostasis at the cellular level as well as at the scale of the whole plant. We have also analyzed the proteins and peptides circulating from shoot to roots in the phloem sap of Fe-deficient plants, identifying several putative new Fe uptake regulators. Our goal is to characterize the molecular mechanism which kickstarts this regulatory loop, and to determine how this mechanism is leveraged by plants to fine-tune the entry of Fe into their roots. This will enable us to understand how plants can sense their Fe status and adjust its transport depending on their needs. Ultimately, we will identify new targets to develop Fe-enriched crops.