Abstract: NRAMP (natural-resistance-associated macrophage) protein family plays an important role in the regulation of heavy metal cadmium (Cd) uptake and transport in plants. Based on conserved sequences of Nramp1 genes from Arabidopsis, rice, tomato and Malus baccata, we designed the degenerate oligonucleotideprimers of the maize Nramp gene. The length of ZmNramp gene identified by cloning and sequencing was 314 bp with 10 exons and encoding 104 amino acids and this gene was named asZmNramp1. By comparing the sequences of Nramp1 gene fragments and amino acids of the above chosen plants, we found that they have the same conserved domains and highly similar oligonucleotide sequences. Bioinformatics analysis results showed that ZmNRAMP1 had molecular weight of 11.5 kD, theoretical pI (protein isoelectric point) of 6.92 and typical transmembrane helical region of transmembrane protein. The RTPCR (reversal transcript polymerase chain reaction) results indicated that the expression of ZmNramp1 gene was significantly up-regulated in the maize seeding roots and leaves treated with different concentrations of cadmium (50, 100 μmol·L^-1 CdCl₂) for 24 h, which was increased by 57% and 83% in roots, and by 26% and 50% in leaves (P<0.05). There was a significantly positive relationship between ZmNramp1 gene expression and Cd content in the seeding roots and leaves of maize, which indicated that the ZmNramp1 gene may be involved in Cd absorption and transportation in maize. Our results provide theoretical basis and genetic resources for maize breeding for heavy metal resistance.

Key words: maize, cadmium transporter, Nramp1 gene, cloning and expression.