Expression and Cellular Localization of ZIP1 Transporter Under Zinc Deficiency in Wild Emmer Wheat

Zinc deficiency is a common problem leading to severe decreases in grain yield and has detrimental effects on nutritional quality in cereals. Wild emmer wheat, Triticum turgidum ssp. dicoccoides, exhibits a potential genetic resource for wheat improvement due to its compatibility with modern wheat. In this study, Zn deficiency response of wild progenitors and modern wheat were examined using molecular and physiological approaches with plants grown under various Zn concentrations. The results revealed wide variation in response to Zn deficiency between wild emmer accessions. Among the wild emmer accessions studied, accession MM 5/4 was found to be most tolerant and accession 19-36 was the most sensitive to Zn deficiency. To better understand Zn transport mechanisms in wild emmer wheat, we analyzed the expression patterns of a ZRT/IRT-like gene, Zrt-, Irt-like protein (ZIP)1, in the roots and shoots of several accessions that were maintained on different concentrations of Zn. Quantitative real-time polymerase chain reaction results revealed that ZIP1 transcript levels are elevated with decreasing Zn supply in all accessions. Particularly, ZIP1 transcript accumulation was lower in the roots of accession MM 5/4 while the susceptible, 19-36 accession, has elevated levels of ZIP1 transcript, revealing a Zn deficiency response for this genotype. We also identified and cloned a full-length ZIP1 transporter, named TdZIP1, and further analyzed the corresponding protein sequence for structural attributes. Under Zn deficiency, deleting the last 20 amino acids from the last transmembrane domain of TdZIP1 and tagging with GFP resulted in endoplasmic reticulum localization. Functional expression of the isolated TdZIP1 using Zn-uptake defective Saccharomyces cerevisiae strains on limiting Zn media showed that it could indeed transport Zn. However, overexpression of this transporter causes excess accumulation of Zn in the cells, thus generating a toxic environment. Overall, our results indicate the possibility of using Triticum dicoccoides for the genetic improvement of zinc deficiency tolerance in wheat.