Cloning and biological function analysis of Nramps in blueberry

The natural resistance-associated macrophage protein (Nramp) family comprises crucial membrane transport proteins that play vital roles in the transport and reuse of heavy metal ions in plants. Limited information is currently available on the Nramp family in blueberry (Vaccinium spp.; Vc). Elucidation of the mechanism underlying mineral-element deficiency and heavy metal toxicity in blueberry is essential for the sustainable development of the blueberry industry. In this study, three Nramp genes (VcNramp4, VcNramp6, and VcNramp8.2) were cloned and identified from blueberry, and their functions were analyzed in transgenic Arabidopsis thaliana and yeast. Sequence analysis showed that the VcNramp genes encoded 321–455 amino acids and contained 6–8 transmembrane structural domains. Expression analysis showed that VcNramp genes were significantly up-regulated under iron (Fe) deficiency. The expression of VcNramp genes was most significantly up-regulated in the roots, by 2.05-fold relative to the control group. VcNramp4 and VcNramp6 expression in yeast and A. thaliana alleviated Fe deficiency stress. Interestingly, yeast expressing VcNramp6 showed a 1.13- to 1.38-fold increase in Fe accumulation at different medium pH levels, which was significantly higher than that of yeast expressing the other VcNramp genes. All VcNramp genes respond to changes in Fe ion concentration. Among them, VcNramp6 can effectively ameliorate Fe deficiency symptoms in plants. The expression of VcNramp genes exhibited distinct tissue specificity. Notably, the expression levels of VcNramp6 and VcNramp8.2 in the stems was only 2 %–10 % of that in the roots. The results illustrated the Fe nutrient inefficiency of blueberry. Furthermore, all identified VcNramp genes responded to mild zinc or cadmium stress, but their expression levels decreased under severe zinc or cadmium stress.