Genome-wide analysis of zinc- and iron-regulated transporter-like protein family members in apple and functional validation of ZIP10.

Deficiency of zinc (Zn) and iron (Fe) is common in apple grown in orchards, which affects fruit yield and quality. However, the mechanisms of absorption and transport of Zn and Fe in apples are still unclear. In the present study, we aimed to identify MdZIP genes and explore the mechanism of response of MdZIPs to Zn and Fe deficiencies. Eighteen Zn- and Fe-regulated transporter-like protein (ZIP) family members were identified in apple (Malus domestica L.) and named according to their chromosomal location. Phylogenetic analysis divided MdZIPs into four groups, and the most closely related MdZIPs in the phylogenetic tree showed similar gene structures and protein motifs. Expression pattern analysis indicated that ZIP genes in apple were differentially expressed among tissues and developmental stages under Zn and Fe deficiency. The overexpression of MdZIP10 increased the content of Zn and Fe in Arabidopsis thaliana L. and MdZIP10 played crucial roles in the uptake and transport of Zn and Fe. MdZIP10 was able to rescue growth of Zn2+ and Fe2+ uptake defective yeast mutants under Zn2+ and Fe2+ deficient conditions, respectively. Symptoms of Zn and Fe deficiency were alleviated in the MdZIP10 transgenic plants. The expression of genes related to Fe and Zn uptake and transport was induced in the MdZIP10 transgenic plants, thereby stimulating endogenous Fe and Zn uptake and transport mechanisms. The present study lays the foundation for future functional analysis of ZIP genes in apple.