Journal Article

Overexpression of phytochelatin synthase in tobacco: distinctive effects of AtPCS1 and CePCS genes on plant response to cadmium

Schat, Henk, Bal, Wojciech, Clemens, Stephan, Hennig, Jacek, Wojas, Sylwia, Skłodowska, Aleksandra, Antosiewicz, Danuta Maria, Kopera, Edyta

2008

Overview

Phytochelatins, heavy-metal-binding polypeptides, are synthesized by phytochelatin synthase (PCS) (EC 2.3.2.15). Previous studies on plants overexpressing PCS genes yielded contrasting phenotypes, ranging from enhanced cadmium tolerance and accumulation to cadmium hypersensitivity. This paper compares the effects of overexpression of AtPCS1 and CePCS in tobacco (Nicotiana tabacum var. Xanthi), and demonstrates how the introduction of single homologous genes affects to a different extent cellular metabolic pathways leading to the opposite of the desired effect. In contrast to WT and CePCS transformants, plants overexpressing AtPCS1 were Cd-hypersensitive although there was no substantial difference in cadmium accumulation between studied lines. Plants exposed to cadmium (5 and 25 μM CdCl2) differed, however, in the concentration of non-protein thiols (NPT). In addition, PCS activity in AtPCS1 transformants was around 5-fold higher than in CePCS and WT plants. AtPCS1 expressing plants displayed a dramatic accumulation of γ-glutamylcysteine and concomitant strong depletion of glutathione. By contrast, in CePCS transformants, a smaller reduction of the level of glutathione was noticed, and a less pronounced change in γ-glutamylcysteine concentration. There was only a moderate and temporary increase in phytochelatin levels due to AtPCS1 and CePCS expression. Marked changes in NPT composition due to AtPCS1 expression led to moderately decreased Cd-detoxification capacity reflected by lower SH:Cd ratios, and to higher oxidative stress (assessed by DAB staining), which possibly explains the increase in Cd-sensitivity. The results indicate that contrasting responses to cadmium of plants overexpressing PCS genes might result from species-dependent differences in the activity of phytochelatin synthase produced by the transgenes.

• Publisher: Oxford University Press,Oxford Publishing Limited (England)
• Subject: Accumulation / Aminoacyltransferases - genetics / Aminoacyltransferases - metabolism / Animals / Arabidopsis - enzymology / Arabidopsis Proteins - genetics / Arabidopsis Proteins - metabolism / biochemical pathways / Biological and medical sciences / Cadmium / Cadmium - metabolism / Cadmium - pharmacology / Caenorhabditis elegans - enzymology / Caenorhabditis elegans Proteins - genetics / Caenorhabditis elegans Proteins - metabolism / Detoxification / Enzymes / Fundamental and applied biological sciences. Psychology / Gene Expression / gene overexpression / Genes. Genome / Glutathione / Heavy metals / Hydroponics / Hypersensitivity / Leaves / metabolic detoxification / metal tolerance / Molecular and cellular biology / Molecular genetics / Nicotiana - genetics / Nicotiana - growth & development / Nicotiana - physiology / Nicotiana tabacum / Oxidative Stress / phenotype / Phenotypes / phytochelatins / Phytochelatins - metabolism / phytotoxicity / Plant Leaves - genetics / Plant Leaves - growth & development / Plant Leaves - metabolism / Plant physiology / plant response / Plant roots / Plant Roots - genetics / Plant Roots - growth & development / Plant Roots - metabolism / Plants / Plants, Genetically Modified - genetics / Plants, Genetically Modified - growth & development / Plants, Genetically Modified - metabolism / Pollution tolerance / polypeptides / Research Papers / Thiols / tobacco / transgenes / γ-glutamylcysteine