Cloning and expression of multiple metallothioneins from hybrid poplar

In an effort to understand processes that are related to heavy metal sequestration, we characterized six metallothionein genes (PtdMTs) in the hybrid cottonwood, Populus trichocarpa x deltoides. cDNA microarrays and reverse transcriptase-polymerase chain reaction were used to examine PtdMT expression in poplar tissues. They displayed differential gene expression patterns, which may be associated with the diverse roles and functions PtdMTs have in coping with particular developmental (e.g. root development and leaf senescence) and environmental cues. The heterologous expression in a cadmium (Cd)-hypersensitive yeast mutant showed the ability of PtdMT cDNAs to confer Cd tolerance. The concentration of PtdMT mRNAs were increased by zinc, but not by copper and Cd. Further studies will help to clarify the role of metallothionein genes in metal homeostasis and poplar development, and help to isolate poplar genotypes particularly tolerant to stress for use in experiments of phytoremediation.