Metallothionein genes from the flowering plant Mimulus guttatus

In response to excess metal, higher plants produce metal‐binding peptides ([γEC] n G) whose biosynthesis is believed to be mediated by enzymes involved in glutathione (γECG) metabolism. In contrast, animals synthesize metallothioneins, gene‐encoded low molecular weight cysteine‐rich metal‐binding proteins. In an investigation of copper‐regulated genes in the copper‐tolerant flowering plant Mimulus guttatus , we have isolated a series of cDNA clones identifying two genes which encode a protein with class I metallothionein domains. This represents the first description of a metallothionein gene in a flowering plant.