Got to hide your Zn away: Molecular control of Zn accumulation and biotechnological applications

• Zn concentrations in plants must be tightly regulated.
• There is large diversity of Zn transporters and Zn chelators.
• Gene expression and copy numbers are altered in Zn hyperaccumulators.
• Zn phytorremediation needs metal accumulators with high biomass.
• Zn biofortification needs marker-assisted breeding and molecular genetics.

Zinc (Zn) is an essential micronutrient for all organisms, with key catalytic and structural functions. Zn deficiency in plants, common in alkaline soils, results in growth arrest and sterility. On the other hand, Zn can become toxic at elevated concentrations. Several studies revealed molecules involved with metal acquisition in roots, distribution within the plant and translocation to seeds. Transmembrane Zn transport proteins and Zn chelators are involved in avoiding its toxic effects. Plant species with the capacity to hyperaccumulate and hypertolerate Zn have been characterized. Plants that accumulate and tolerate high amounts of Zn and produce abundant biomass may be useful for phytoremediation, allowing cleaning of metal-contaminated soils. The study of Zn hyperaccumulators may provide indications of genes and processes useful for biofortification, for developing crops with high amounts of nutrients in edible tissues. Future research needs to focus on functional characterization of Zn transporters in planta, elucidation of Zn uptake and sensing mechanisms, and on understanding the cross-talk between Zn homeostasis and other physiological processes. For this, new research should use multidisciplinary approaches, combining traditional and emerging techniques, such as genome-encoded metal sensors and multi-element imaging, quantification and speciation using synchrotron-based methods.