Zn is an essential micronutrient for all living organisms. It plays key catalytic and structural roles in a myriad of proteins. However, Zn deficiency is the most widespread crop micronutrient deficiency. Gaining insights into the molecular mechanisms of Zn homeostasis can help achieving Zn biofortification in crops, and alleviate the global Zn deficiency problems. Plants rely on elaborate regulatory mechanisms to cope with Zn deficiency in the soil. In A. thaliana, the F group basic leucine zipper (F-bZIP) transcription factors (TFs) bZIP19 and bZIP23, are the central regulators of the Zn deficiency response. Under Zn deficiency, these TFs bind to the promoter of their target genes and activate their transcription. The target genes are mainly members from the Zrt/Irt-like Protein (ZIP) and Nicotianamine Synthase (NAS) families, involved in Zn transport and distribution, respectively, which contribute to the plant response to Zn deficiency. Under Zn sufficiency, Zn ions bind to the Zn-Sensor Motif (ZSM) of these TFs, which also act as Zn sensors, impairing their target gene transcriptional activation. Mutations in the ZSM leads to increased Zn content in A. thaliana leaves and seeds. In addition, there is evidence of conservation of the F-bZIPregulated Zn deficiency response in land plants, which makes this regulatory network an attractive target for plant Zn biofortification in translational approaches to crops. Legume species are an important source of micronutrients and proteins in human diets, deserving attention as targets for Zn biofortification efforts. The first aim of this thesis was to dissect the molecular mechanism of Zn deficiency response in the model legume, Medicago truncatula. In this context, the M. truncatula F-bZIPs were identified and functionally characterized. Through gene expression, heterologous complementation and subcellular localization analyses, I show that MtFbZIP1 is the functional homolog of AtbZIP19/23, whereas MtFbZIP2 does not playing a role in the Zn deficiency response. Tissue expression analyses with MtFbZIP1/2 and selected MtZIP genes in M. truncatula plants and root nodules indicate a role in Zn transport and Zn homeostasis regulation in these tissues. Additionally, I developed a protocol for stable transformation of M. truncatula leaf explants aiming at obtaining MtFbZIP1 knockout mutant. Taken together, the results support the conservation of the F-bZIP-regulated Zn deficiency response in M. truncatula. Metal hyperaccumulator species, including Zn hyperaccumulators naturally accumulate extremely high concentration of metals/Zn in their aboveground tissues. Knowledge on the molecular basis of Zn hyperaccumulation can contribute to developing Zn biofortification strategies. The second aim of this thesis was to identify and investigate the F-bZIP TFs in two Zn hyperaccumulator model species from the Brassicaceae family, Arabidopsis halleri and Noccaea caerulescens. Protein functional characterization and comparative protein sequence analyses suggested that the F-bZIP-regulated Zn deficiency response is conserved in these two model species. Results indicate that AhbZIP23 and NcbZIP19/23 are the functional homologs of AtbZIP19/23 in A. halleri and N. caerulescens, respectively. In addition, we propose a role for one AhbZIP19 variant, which has a modified ZSM, in the Zn hyperaccumulation trait in A. halleri. Overall, the results provide novel information on the Zn homeostasis regulation mechanisms in the legume model M. truncatula, and the Zn hyperaccumulator models A. halleri and N. caerulescens. This work paves the way for delivering Zn biofortification in crops and contributes to the tackling of worldwide Zn deficiency in human diets.