Exploiting plants for glutathione (GSH) production: Uncoupling GSH synthesis from cellular controls results in unprecedented GSH accumulation

Abstract

Summary Glutathione (GSH) is a key factor for cellular redox homeostasis and tolerance against abiotic and biotic stress (May et al., 1998; Noctor et al., 1998a). Previous attempts to increase GSH content in plants have met with moderate success (Rennenberg et al., 2007), largely because of tight and multilevel control of its biosynthesis (Rausch et al., 2007). Here, we report the in planta expression of the bifunctional γ‐glutamylcysteine ligase—glutathione synthetase enzyme from Streptococcus thermophilus (StGCL‐GS), which is shown to be neither redox‐regulated nor sensitive to feedback inhibition by GSH. Transgenic tobacco plants expressing StGCL‐GS under control of a constitutive promoter reveal an extreme accumulation of GSH in their leaves (up to 12 μmol GSH/gFW, depending on the developmental stage), which is more than 20‐ to 30‐fold above the levels observed in wild‐type (wt) plants and which can be even further increased by additional sulphate fertilization. Surprisingly, this dramatically increased GSH production has no impact on plant growth while enhancing plant tolerance to abiotic stress. Furthermore, StGCL‐GS‐expressing plants are a novel, cost‐saving source for GSH production, being competitive with current yeast‐based systems (Li et al., 2004).

Ascorbate and Glutathione: The Heart of the Redox Hub

“…No lesions were observed in poplar (Populus sp.) with similar increases in tissue glutathione (Noctor and Foyer, 1998), and it has recently been shown that very high glutathione contents can be engineered in tobacco without major detrimental effects on plant development (Liedschulte et al, 2010). Thus, the available data suggest that high levels of glutathione can be tolerated by plants and are not in themselves sufficient to trigger cell death pathways.…”

Glutathione regulates ACC synthase transcription via WRKY33 and ACC oxidase by modulating mRNA stability to induce ethylene synthesis during stress

“…2004; Mullineaux and Rausch, 2005;Liedschulte et al, 2010). Transgenic Arabidopsis plants with low GSH level (10% of the wild type) exhibit hypersensitivity to cadmium stress due to the limited capacity of these plants to make phytochelatins (Xiang et al, 2001).…”

Overaccumulation of γ-Glutamylcysteine in a Jasmonate-Hypersensitive Arabidopsis Mutant Causes Jasmonate-Dependent Growth Inhibition

“…Although jah2 has only 4.5 times more g-EC than the normal amount of GSH, and g-EC level in jah2 pad2-1 is equal to that of GSH in the wild type, both are compromised in growth. By contrast, GSH up to 20-fold higher than normal in transgenic tobacco (Nicotiana tabacum) plants expressing a bifunctional g-EC-ligase/ GSH-S had no phenotypic effect (Liedschulte et al, 2010). On the other hand, overexpression of a g-ECligase in tobacco resulting in up to 25-fold elevated g-EC yielded plants displaying pathogenesis-related necrotic lesions, although these plants also had 3 to 5 times the normal GSH level (Creissen et al, 1999).…”