Evidence for the participation of a 5-oxo-prolinase in degradation of glutathione in Nicotiana tabacum

Environmental metabolomics links genotype to phenotype and predicts genotype abundance in wild plant populations

'The Holy Grail' of plant ecology is to uncover rules that associate species and traits with environmental constraints, community composition and subsequent ecosystem functioning. These aims have been crystallized in recent years within the context of global climate change and environmental pollution, increasing the urgency of the need to predict how vegetation will respond across spatial scales. We investigated whether genetic diversity is associated with the way in which phenotypic plasticity within plant populations is realized and whether this is related to genotype abundance. We used environmental metabolomics to demonstrate biochemical variation between co-occurring genotypes of Carex caryophyllea L. A novel combined metabolomic/functional trait analysis was used to test the functionality of this variation in governing plasticity to variation in edaphic conditions, with particular reference to metabolic pathways that play important roles in growth-related traits. We show that genetic diversity within a wild C. caryophyllea population relates to differences in metabolic composition and functional traits in response to soil nutrient variation, influencing genotype abundance within a community. Our findings highlight the vital role genetic diversity plays within a population in facilitating plant phenotypic plasticity and the potential usefulness of environmental metabolomics to future ecological studies.

Localization of members of the gamma-glutamyl transpeptidase family identifies sites of glutathione and glutathione S-conjugate hydrolysis

gamma-Glutamyl transpeptidases (GGTs) are essential for hydrolysis of the tripeptide glutathione (gamma-glutamate-cysteine-glycine) and glutathione S-conjugates since they are the only enzymes known to cleave the amide bond linking the gamma-carboxylate of glutamate to cysteine. In Arabidopsis thaliana, four GGT genes have been identified based on homology with animal GGTs. They are designated GGT1 (At4g39640), GGT2 (At4g39650), GGT3 (At1g69820), and GGT4 (At4g29210). By analyzing the expression of each GGT in plants containing GGT:beta-glucuronidase fusions, the temporal and spatial pattern of degradation of glutathione and its metabolites was established, revealing appreciable overlap among GGTs. GGT2 exhibited narrow temporal and spatial expression primarily in immature trichomes, developing seeds, and pollen. GGT1 and GGT3 were coexpressed in most organs/tissues. Their expression was highest at sites of rapid growth including the rosette apex, floral stem apex, and seeds and might pinpoint locations where glutathione is delivered to sink tissues to supplement high demand for cysteine. In mature tissues, they were expressed only in vascular tissue. Knockout mutants of GGT2 and GGT4 showed no phenotype. The rosettes of GGT1 knockouts showed premature senescence after flowering. Knockouts of GGT3 showed reduced number of siliques and reduced seed yield. Knockouts were used to localize and assign catalytic activity to each GGT. In the standard GGT assay with gamma-glutamyl p-nitroanilide as substrate, GGT1 accounted for 80% to 99% of the activity in all tissues except seeds where GGT2 was 50% of the activity. Protoplasting experiments indicated that both GGT1 and GGT2 are localized extracellularly but have different physical or chemical associations.

Glutathione, Altruistic Metabolite in Fungi

Glutathione (GSH; gamma-L-glutamyl-L-cysteinyl-glycine), a non-protein thiol with a very low redox potential (E'0 = 240 mV for thiol-disulfide exchange), is present in high concentration up to 10 mM in yeasts and filamentous fungi. GSH is concerned with basic cellular functions as well as the maintenance of mitochondrial structure, membrane integrity, and in cell differentiation and development. GSH plays key roles in the response to several stress situations in fungi. For example, GSH is an important antioxidant molecule, which reacts non-enzymatically with a series of reactive oxygen species. In addition, the response to oxidative stress also involves GSH biosynthesis enzymes, NADPH-dependent GSH-regenerating reductase, glutathione S-transferase along with peroxide-eliminating glutathione peroxidase and glutaredoxins. Some components of the GSH-dependent antioxidative defence system confer resistance against heat shock and osmotic stress. Formation of protein-SSG mixed disulfides results in protection against desiccation-induced oxidative injuries in lichens. Intracellular GSH and GSH-derived phytochelatins hinder the progression of heavy metal-initiated cell injuries by chelating and sequestering the metal ions themselves and/or by eliminating reactive oxygen species. In fungi, GSH is mobilized to ensure cellular maintenance under sulfur or nitrogen starvation. Moreover, adaptation to carbon deprivation stress results in an increased tolerance to oxidative stress, which involves the induction of GSH-dependent elements of the antioxidant defence system. GSH-dependent detoxification processes concern the elimination of toxic endogenous metabolites, such as excess formaldehyde produced during the growth of the methylotrophic yeasts, by formaldehyde dehydrogenase and methylglyoxal, a by-product of glycolysis, by the glyoxalase pathway. Detoxification of xenobiotics, such as halogenated aromatic and alkylating agents, relies on glutathione S-transferases. In yeast, these enzymes may participate in the elimination of toxic intermediates that accumulate in stationary phase and/or act in a similar fashion as heat shock proteins. GSH S-conjugates may also form in a glutathione S-transferases-independent way, e.g. through chemical reaction between GSH and the antifugal agent Thiram. GSH-dependent detoxification of penicillin side-chain precursors was shown in Penicillium sp. GSH controls aging and autolysis in several fungal species, and possesses an anti-apoptotic feature.