Expression of a rice Zn transporter, OsZIP1, increases Zn concentration in tobacco and finger millet transgenic plants

Zinc (Zn) deficiency is very widespread both from the plant and human nutrition perspective. One of the approaches to improve Zn in crop plants is by over-expression of Zn transporters such that plants can uptake and accumulate additional Zn added to soil. The ZIP family transporters generally contribute to Zn homeostasis in plants by regulating Zn transport into the cell. We over-expressed OsZIP1 in finger millet and model plant tobacco under the control of constitutive (35S) and endosperm-specific (Bx17) promoters to study the improvement in Zn accumulation. The transcript analysis revealed the induction of ZIP1 in leaf and root tissue under Zn deprivation in finger millet cultivars. Ectopic expression of OsZIP1 in tobacco under CaMV35S (n35S) and Bx17 (nBx17) improved seed Zn concentration compared to untransformed wild-type plants. In addition, we successfully developed finger millet transgenic plants, f35S and fBx17, expressing the OsZIP1 under 35S (f35S) and Bx17 (fBx17) promoter, respectively. The transgenic plants accumulated significantly higher Zn in seeds compared to untransformed wild-type finger millet plants. Plants expressing the gene under Bx17 promoter accumulated more Zn in seed than 35S plants. Apart from Zn, finger millet transgenic plants also showed increased Mn content in seeds. Our results show the involvement of OsZIP1 in improving Zn concentration in tobacco and finger millet. Using endosperm-specific promoter, it is possible to improve the seed Zn concentration in the edible part of cereals.