Zinc Biofortification: Role of ZIP Family Transporters in the Uptake of Zinc from the Soil up to the Grains

It is a known fact that plants and animals need micronutrients like zinc (Zn) for their proper growth and development. Zinc plays a significant role as activator of many enzymes, in biosynthetic pathway of several biomolecules and regulative and protective functions in plants. Its poor availability in soils causes low crop yield and low Zn content in food grains which often promotes adverse effects on human health. Therefore, this overview describes the role of transporters in the plant physiological processes that maintain the Zn homeostasis. It includes absorption of Zn from the soil via roots, control of Zn transport from roots to aerial plant parts. Soil condition play significant role in availability of Zn to the plant roots for absorption, thereafter transporters facilitate their translocation up to the grains. Zinc homeostasis is highly regulated in a complex process. The families of Zn-regulated transporter (ZIP)-like proteins are involved in the cellular uptake of Zn, as well as its intracellular trafficking and detoxification in plants. Very little information is available on the structural features and Zn transport mechanisms of plant ZIP family transporters (ZRT-IRT-like proteins). In this overview, we elucidate a comprehensive structure, functions, and regulations of ZIP carriers. We also described the structure of plant ZIPs through homology modeling and multiple sequence alignment with Bordetella bronchiseptica ZIP (BbZIP) protein whose crystal structure has been solved recently. The details on ZIP transporter genes identified and characterized in some plants till date may play crucial role in biofortification of Zn in food grains.