Regulation of the Phytochelatin Synthase Gene <italic>AtPCS2 </italic>in <italic>Arabidopsis thaliana</italic>

Abstract

Phytochelatin synthase (PCS) plays an essential role in heavy metal detoxification in plants and fungi, via the catalyzation of phytochelatins (PCs) biosynthesis from the substrate of glutathione (GSH). Two PCS genes <italic>AtPCS1</italic> and <italic>AtPCS2</italic> are present in <italic>Arabidopsis</italic> genome. However, loss of function of only the <italic>AtPCS1</italic> gene resulted in undetectable PCs and the consequent metal hypersensitivity in the corresponding mutant <italic>cad1</italic>-<italic>3</italic>,while <italic>in vitro</italic> assay indicated that AtPCS2 is capable to efficiently catalyze PCs biosynthesis. These results suggest that repression mechanisms exist in <italic>Arabidopsis</italic> to tightly control <italic>AtPCS2</italic> function <italic>in vivo</italic>. To test and decipher this hypothesis, we generated the construct 35S/AtPCS2::cMyc and transformed it into the PCs-deficient mutant <italic>cad1</italic>-<italic>3</italic>. Our results showed that both the <italic>AtPCS2</italic> mRNA and protein levels were steadily high in the transgenic plants. Consistently, PCs biosynthesis and metal tolerance were also observed when <italic>AtPCS2</italic> was introduced into <italic>cad1</italic>-<italic>3</italic>. Furthermore, in addition to the cytosol, AtPCS2 was also localized to the nuclei. Taken together, all these results indicate that <italic>AtPCS2</italic> is under tight control mainly at the transcription level in <italic>Arabidopsis</italic>, and it may function beyond catalyzing PCs biosynthesis.