Expression of a Neurospora crassa zinc transporter gene in transgenic Nicotiana tabacum enhances plant zinc accumulation without co-transport of cadmium

Zinc (Zn) is an essential micronutrient required for growth and development of all organisms. Deficiency of Zn in humans is widespread, affecting 25% of world population and efforts are underway to develop crop plants with high levels of Zn in their edible parts. When strategies for enhancing Zn in crop plants are designed, it is essential to exclude cadmium (Cd), a toxic analogue of Zn. In the present work, a high affinity and high specificity zinc transporter gene (tzn1) from Neurospora crassa was cloned and introduced into Nicotiana tabacum with the objective of enhancing the potential of plants for zinc acquisition. When grown in hydroponic medium spiked with ⁶⁵Zn, transgenic plants showed enhanced accumulation of Zn (up to 11 times) compared to control plants, which was confirmed further by environmental scanning electron microscopy coupled with Energy Dispersive X-ray analysis. More importantly, no significant difference in uptake of Cd²⁺, Fe²⁺, Ni²⁺, Cu²⁺, Mn²⁺ and Pb²⁺ between the transgenic and control plants was observed. The present studies have shown that Neurospora crassa tzn1 is a potential candidate gene for developing transgenic plants for improving Zn uptake, without co-transport of Cd and may have implications in Zn phytofortification and phytoremediation.