Showing papers by "Christine H. Foyer published in 2010"

A nuclear glutathione cycle within the cell cycle

Abstract: The complex antioxidant network of plant and animal cells has the thiol tripeptide GSH at its centre to buffer ROS (reactive oxygen species) and facilitate cellular redox signalling which controls growth, development and defence GSH is found in nearly every compartment of the cell, including the nucleus Transport between the different intracellular compartments is pivotal to the regulation of cell proliferation GSH co-localizes with nuclear DNA at the early stages of proliferation in plant and animal cells Moreover, GSH recruitment and sequestration in the nucleus during the G1- and S-phases of the cell cycle has a profound impact on cellular redox homoeostasis and on gene expression For example, the abundance of transcripts encoding stress and defence proteins is decreased when GSH is sequestered in the nucleus The functions of GSHn (nuclear GSH) are considered in the present review in the context of whole-cell redox homoeostasis and signalling, as well as potential mechanisms for GSH transport into the nucleus We also discuss the possible role of GSHn as a regulator of nuclear proteins such as histones and PARP [poly(ADP-ribose) polymerase] that control genetic and epigenetic events In this way, a high level of GSH in the nucleus may not only have an immediate effect on gene expression patterns, but also contribute to how cells retain a memory of the cellular redox environment that is transferred through generations

Plant homologs of the Plasmodium falciparum chloroquine-resistance transporter, PfCRT, are required for glutathione homeostasis and stress responses

Abstract: In Arabidopsis thaliana, biosynthesis of the essential thiol antioxidant, glutathione (GSH), is plastid-regulated, but many GSH functions, including heavy metal detoxification and plant defense activation, depend on cytosolic GSH. This finding suggests that plastid and cytosol thiol pools are closely integrated and we show that in Arabidopsis this integration requires a family of three plastid thiol transporters homologous to the Plasmodium falciparum chloroquine-resistance transporter, PfCRT. Arabidopsis mutants lacking these transporters are heavy metal-sensitive, GSH-deficient, and hypersensitive to Phytophthora infection, confirming a direct requirement for correct GSH homeostasis in defense responses. Compartment-specific measurements of the glutathione redox potential using redox-sensitive GFP showed that knockout of the entire transporter family resulted in a more oxidized glutathione redox potential in the cytosol, but not in the plastids, indicating the GSH-deficient phenotype is restricted to the cytosolic compartment. Expression of the transporters in Xenopus oocytes confirmed that each can mediate GSH uptake. We conclude that these transporters play a significant role in regulating GSH levels and the redox potential of the cytosol.

Recruitment of glutathione into the nucleus during cell proliferation adjusts whole‐cell redox homeostasis in Arabidopsis thaliana and lowers the oxidative defence shield

Abstract: Summary Cellular redox homeostasis and signalling are important in progression of the eukaryotic cell cycle. In animals, the low-molecular-weight thiol tripeptide glutathione (GSH) is recruited into the nucleus early in the cell proliferation cycle. To determine whether a similar process occurs in plants, we studied cell proliferation in Arabidopsis thaliana. We show that GSH co-localizes with nuclear DNA during the proliferation of A. thaliana cells in culture. Moreover, GSH localization in the nucleus was observed in dividing pericycle cells of the lateral root meristem. There was pronounced accumulation of GSH in the nucleus at points in the growth cycle at which a high percentage of the cells were in G1 phase, as identified by flow cytometry and marker transcripts. Recruitment of GSH into the nucleus led to a high abundance of GSH in the nucleus (GSHn) and severe depletion of the cytoplasmic GSH pool (GSHc). Sequestration of GSH in the nucleus was accompanied by significant decreases in transcripts associated with oxidative signalling and stress tolerance, and an increase in the abundance of hydrogen peroxide, an effect that was enhanced when the dividing cells were treated with salicylic acid. Total cellular GSH and the abundance of GSH1 and GSH2 transcripts increased after the initial recruitment of GSH into the nucleus. We conclude that GSH recruitment into the nucleus during cell proliferation has a profound effect on the whole-cell redox state. High GSHn levels trigger redox adjustments in the cytoplasm, favouring decreased oxidative signalling and enhanced GSH synthesis.

Conditional modulation of NAD levels and metabolite profiles in Nicotiana sylvestris by mitochondrial electron transport and carbon/nitrogen supply.

Abstract: Environmental controls on leaf NAD status remain poorly understood. Here, we analyzed the effects of two key environmental variables, CO2 and nitrogen, on leaf metabolite profiles, NAD status and the abundance of key transcripts involved in de novo NAD synthesis in wild-type (WT) Nicotiana sylvestris and the CMSII mutant that lacks respiratory complex I. High CO2 and increased N supply both significantly enhanced NAD+ and NADH pools in WT leaves. In nitrogen-sufficient conditions, CMSII leaves were enriched in NAD+ and NADH compared to the WT, but the differences in NADH were smaller at high CO2 than in air because high CO2 increased WT NADH/NAD+. The CMSII-linked increases in NAD+ and NADH status were abolished by growth with limited nitrogen, which also depleted the nicotine and nicotinic acid pools in the CMSII leaves. Few statistically significant genotype and N-dependent differences were detected in NAD synthesis transcripts, with effects only on aspartate oxidase and NAD synthetase mRNAs. Non-targeted metabolite profiling as well as quantitative amine analysis showed that NAD+ and NADH contents correlated tightly with leaf amino acid contents across all samples. The results reveal considerable genotype- and condition-dependent plasticity in leaf NAD+ and NADH contents that is not linked to modified expression of NAD synthesis genes at the transcript level and show that NAD+ and NADH contents are tightly integrated with nitrogen metabolism. A regulatory two-way feedback circuit between nitrogen and NAD in the regulation of N assimilation is proposed that potentially links the nutritional status to NAD-dependent signaling pathways.