Functional complementation in yeast mutant strains. The Zn and Fe transportation mutant zrt1zrt2 (A) and fet3fet4 (B) were transformed with the expression vector pFL61 carrying ZmZIP1-ZmZIP8, ZmIRT1 and the functional characterized ZIP genes, OsZIP5, OsZIP8 and OsIRT1. The wild type strain DY1455 transformed with pFL6 was applied as a positive control, and the yeast mutant transformed with empty vector pFL61 was used as a negative control. The transformed yeast cells were grown under different metal conditions as indicated, and the transformed fet3fet4 was grown on medium with pH 5.8. Cell concentration was adjusted to OD600 = 1 and serial dilutions (1.0, 0.1, 0.01 and 0.001) were made. For assay, 5-μL of each dilution was spotted on plates and grown for 6 days at 30°C.