Characterization of γ-glutamyltransferase- and phytochelatin synthase-mediated catabolism of glutathione and glutathione <i>S</i>-conjugates in <i>Arabidopsis thaliana</i>

Abstract

Glutathione (GSH, γ-L-glutamyl-L-cysteinyl-glycine) has been implicated in a multitude of cellular functions, such as protection of cells against oxidative stress, detoxification of xenobiotics via degradation of GSH S-conjugates, and disease resistance. Glutathione also serves as a precursor of phytochelatins, and thereby plays an essential role in heavy metal detoxification. The Arabidopsis genome encodes three functional γ-glutamyltransferase genes (AtGGT1, AtGGT2, AtGGT4) and two phytochelatin synthase genes (AtPCS1, AtPCS2). The function of plant GGT has not yet been clearly defined, although it is thought to be involved in GSH and GSH S-conjugate catabolism. On the other hand, besides its role in heavy metal detoxification, PCS has also been involved in GSH S-conjugate catabolism. Herein we describe the HPLC characterization of GSH and GSH S-conjugate catabolism in Arabidopsis mutants deficient in GSH biosynthesis (pad2-1/ gsh1), atggt and atpcs1 T-DNA insertion mutants, atggt pad2-1, atggt atpcs1 double mutants, and the atggt1 atggt4 atpcs1 triple mutant. The results of our HPLC analysis confirm that AtGGT and AtPCS play important roles in two different pathways related with GSH and GSH S-conjugate (GS-bimane) catabolism in Arabidopsis.

Phytochelatins: Sulfur-Containing Metal(loid)-Chelating Ligands in Plants

“…The constitutive expression of PCS [292] and the presence of homologues of the PCS gene(s) in plants growing in ecosystems geographically remote from metal-contaminated sites, as well as in representatives of various kingdoms of living organisms, suggest that PCS has a wide range of different functions [124]. In addition to a response to metalinduced stress, PCS is a cysteine peptidase that regulates the catabolism of glutathione and glutathione conjugates in the cytosol [228,242,293]. As a result, the glycine residue is cleaved off from the conjugates, similarly to how it occurs during the biosynthesis of PCs.…”