Molecular basis of zin homeostasis in Arabidopsis and Brachypodium model plants

Zinc (Zn) is an essential micronutrient for all life forms. Zn has a cofactor role in all classes of enzymes and is involved in multiple molecular, cellular and physiological functions. Plants, and crops in particular, also need enough amount of this transition metal for their growth and for yield produc-tion. They are additionally an important source of Zn for animals and humans and around two billion people are depending on legumes and grains as their main Zn source. Zn is however toxic for plants at high concentrations. The eudicot Arabidopsis thaliana (Arabidopsis) and monocot rice model spe-cies have been widely used for physiological and molecular studies of Zn homeostasis under various Zn regimes. These studies have resulted in the identification and characterization of multiple gene families of Zn transporters, the most important of which is ZRT, IRT-like Protein (ZIP) family. How-ever, the sophisticated signaling and regulation mechanisms behind Zn uptake, transport and translo-cation in plants remain unclear. Aiming at revealing these mechanisms, our group has dissected the dynamic response to changes in Zn depletion and resupply. First, time-resolved sampling strategy in Arabidopsis allowed concomitant quantification of the dynamics of Zn uptake, microsomal and solu-ble proteins, and specific transcripts, in space (root and shoot) and time. Zn-responding signaling/reg-ulatory molecules included receptor and MAP kinases, calcium signaling proteins, phosphoinositides, G-proteins, COP9 signalosome members, as well as multiple transcription factors. We selected a list of candidate proteins and upon phenotyping the mutant lines, further characterized three final candi-dates. This part of the work was however unsuccessful to identify a clear link between candidate pro-teins and Zn homeostasis in Arabidopsis. Second, we aimed at investigating Zn homeostasis in mon-ocot model plant Brachypodium distachyon (Brachypodium). Although some important players of Zn uptake and transport have been studied in wheat, barley and especially rice, it is unclear how different or similar are the responses of monocots and eudicots to Zn supply at the molecular level. Rice, on the other hand, is not an ideal and perfect model of Zn/iron studies for all monocots. We studied the physiological, ionome and transcriptome response of Brachypodium to static and dynamic Zn supply. Our studies showed that Brachypodium responds to Zn deficiency and excess in all the mentioned levels and has a high potential to be extensively used as a model plant in Zn studies for monocots especially for wheat and barley. Moreover, we showed that ZIP family genes are strongly regulated in shoot upon Zn resupply before any Zn was translocated to shoot, which is indicative of root-to-shoot signaling. Collectively, we showed that studying rapid molecular response of plants to Zn resupply after deficiency reveals new aspects of the Zn homeostasis network. We also introduce Brachypodium as a new and efficient model for Zn studies