Cloning and Molecular Characterization of the Zinc Transporter (ZIP) Gene from Cassava

Abstract

               The zinc transporter (ZIP) involved in zinc uptake, controls the major steps in growth development tissue. In this study, cassava (Manihot esculenta Crantz var. HB80) ZIP cDNA of 726 bp length was isolated from developing fibrous roots during growth in tissue culture. This gene was highly homologous with those from other plant species. DNA blot analysis indicated that at least two copies of ZIP are present in the cassava genome. Three Thai cassava varieties, namely Huaybong 80 (HB80), Kasetsart 50 (KU50) and Rayong 1 (R1) were used to evaluate the steady-state transcript accumulation of transporter genes in a tissue culture experiment. Their agronomic characters were also observed. Total dry weight (TDW) of each variety was found to be highest after eight weeks culture with 0.15 mM ZnSO₄.7H₂O added to the culture medium. The lengths of leaves, petioles, stems and fibrous roots were all found to be greatest with this treatment level.

                A high differential expression of the ZIP gene in different tissue media was observed in the stems, fibrous roots and leafs, respectively. The results showed that the levels of ZIP genes were high in the treatment containing 0 mM and 0.15 mM of ZnSO₄.7H₂O, which was reflected by the highest fresh mass, dry mass, leaf number, fibrous root number, leaf length, stem length, petiole length and fibrous root length with the 0.15 mM ZnSO₄.7H₂O treatment. The high level expression of these genes was most pronounced five to six weeks after harvest, because the plants used more nutrients at the start of growth development. The levels of these genes in R1 showed a higher level of expression than those of KU50 and HB80, reflected by R1 having the highest fresh mass when compared with KU50 and HB80.