Zinc transport mediated by barley ZIP proteins are induced by low pH

It is estimated that nearly 50% of the world's population is at risk of zinc (Zn) deficiency. The challenge is therefore to increase the Zn content in edible plant parts in order to improve the nutritional value of staple foods. We recently reported the identification and characterization of three barley genes encoding zinc transport proteins belonging to the ZIP protein family. These proteins are believed to be involved in cellular uptake of Zn(2+). In this addendum, the Zn(2+) transport capacity of ZIP proteins isolated from barley roots was investigated in response to various pH levels. We show that a lowering of pH induces a better growth at low Zn(2+) concentrations of yeast cells expressing ZIP proteins. However, no significant change in transport capacity (V(max)) could be observed for HvIRT1, whereas lowering of pH from 5.5 to 4.2 increased the V(max) value with 64% for HvZIP5. These results indicate that proton activity has an important role in regulating the Zn(2+) transport capacity of Zn(2+) specific ZIP transport proteins. This information will increase the understanding of ZIP proteins and facilitate engineering of genotypes able to grow efficiently on marginal soils.