Effect of cadmium on gene expression in the liverwort Lunularia cruciata

Bryophytes are valuable bioaccumulators, because they have high absorbing and ion exchange capacities. Cadmium (Cd) is a heavy metal naturally present in soil; it is non-essential and highly toxic to most organisms, having toxicity 2 to 20 times higher than many other heavy metals. The presence of elevated levels of Cd ions triggers a wide range of cellular responses including changes in gene expression and synthesis of metal-detoxifying peptides. To investigate the ability of Cd to affect gene transcription, the messenger RNA (mRNA) differential display technique was applied to the identification and isolation of genes whose transcription was altered in cultured Lunularia cruciata plants that were grown in the presence of cadmium salts. Four genes whose mRNA levels significantly changed in response to cadmium exposure were isolated and identified. The first gene identified in our analysis is up-regulated by Cd: it encodes the enzyme cystathionine γ-synthase. The other genes are down-regulated by cadmium. These genes encode a methyltransferase, a tyrosine phosphatase and the EST 408 of the diatom Fragilariopsis cylindrus, whose function is unknown. Our findings demonstrate the usefulness of mRNA differential display technique for the detection of plant metabolic pathways affected by cadmium stress.