Molecular Characterization and Tissue Expression of Common Tobacco ( Nicotiana tabacum ) Cadmium Resistance Protein 2 and Metal Tolerance Protein 4 Genes

The complete coding sequences of common tobacco cadmium resistance protein 2 and metal tolerance protein 4 genes were amplified by RT-PCR. The tobacco cadmium resistance protein 2 gene encodes a protein of 192 amino acids which shares high identity with the cadmium resistance protein 2 of four species— nicotiana tomentosiformis (99%), wood tobacco (97%), capsicum annuum (90%) and potato (86%). The tobacco metal tolerance protein 4 gene encodes a protein of 415 amino acids which shares high identity with the metal tolerance protein 4 of six species— nicotiana tomentosiformis (90%), wood tobacco (90%), lycopersicon esculentum (84%), potato (84%), lycopersicon pennellii (83%) and capsicum annuum (82%). Prediction of transmembrane helices showed that cadmium resistance protein 2 and metal tolerance protein 4 might be two transmembrane proteins. Phylogenetic analysis revealed that the common tobacco cadmium resistance protein 2 and metal tolerance protein 4 genes both have a closer genetic relationship with the wood tobacco cadmium resistance protein 2 and metal tolerance protein 4 genes. Computer-assisted analysis showed that cadmium resistance protein 2 gene is structured in 4 exons and 3 introns and metal tolerance protein 4 gene consists of 7 exons and 6 introns. The gene expression profile analysis indicated that the common tobacco cadmium resistance protein 2 and metal tolerance protein 4 genes were highly expressed in root.