Cloning and characterisation of ZmZLP1, a gene encoding an endoplasmic reticulum-localised zinc transporter in Zea mays

The ZmZLP1 (ZmZIP-like protein) gene was isolated from a cDNA library of Zea mays L. (maize) pollen. Bioinformatics analysis indicated that ZmZLP1 shares many characteristics of the ZIP (ZRT/IRT-like protein) family of metal ion transporters. Under general nutrient conditions, the expression of ZmZLP1 was detected in both mature pollen and, less strongly, in male inflorescences, whereas an induction of the ZmZLP1 transcript was observed in roots after 12 h of zinc deprivation. The visualisation of GFP showed that ZmZLP1 was targeted to the endoplasmic reticulum (ER). To investigate the gene's functions, we fused ZmZLP1 with the signal peptide of the plasma membrane-localised protein AtIRT1 and transformed this fusion protein into the zinc uptake-deficient yeast (Saccharomyces cerevisiae) strain ZHY3 and the wild-type strain DEY1457. The IRT1-ZmZLP1 transformants grew poorly on zinc-limited medium, and this growth defect was rescued by zinc supplementation, suggesting that ZmZLP1 is responsible for transporting zinc from the ER to the cytoplasm. Further research indicated that ZmZLP1 is involved in the unfolded protein response (UPR) pathway and enhances the heat resistance of yeast cells.