Glutathione contributes to plant defence against parasitic cyst nematodes

Cyst nematodes (CNs) are an important group of root-infecting sedentary endoparasites that severely damage many crop plants worldwide. An infective CN juvenile enters the host's roots and migrates towards the vascular cylinder, where it induces the formation of syncytial feeding cells, which nourish the CN throughout its parasitic stages. Here, we examined the role of glutathione (l-gamma-glutamyl-l-cysteinyl-glycine) in Arabidopsis thaliana on infection with the CN Heterodera schachtii. Arabidopsis lines with mutations pad2, cad2, or zir1 in the glutamate-cysteine ligase (GSH1) gene, which encodes the first enzyme in the glutathione biosynthetic pathway, displayed enhanced CN susceptibility, but susceptibility was reduced for rax1, another GSH1 allele. Biochemical analysis revealed differentially altered thiol levels in these mutants that was independent of nematode infection. All glutathione-deficient mutants exhibited impaired activation of defence marker genes as well as genes for biosynthesis of the antimicrobial compound camalexin early in infection. Further analysis revealed a link between glutathione-mediated plant resistance to CN infection and the production of camalexin on nematode infection. These results suggest that glutathione levels affect plant resistance to CN by fine-tuning the balance between the cellular redox environment and the production of compounds related to defence against infection

Chloroplasts require glutathione reductase to balance reactive oxygen species and maintain efficient photosynthesis

Thiol-based redox-regulation is vital for coordinating chloroplast functions depending on illumination and has been throroughly investigated for thioredoxin-dependent processes. In parallel, glutathione reductase (GR) maintains a highly reduced glutathione pool, enabling glutathione-mediated redox buffering. Yet, how the redox cascades of the thioredoxin and glutathione redox machineries integrate metabolic regulation and detoxification of reactive oxygen species remains largely unresolved because null mutants of plastid/mitochondrial GR are embryo-lethal in Arabidopsis thaliana. To investigate whether maintaining a highly reducing stromal glutathione redox potential (E-GSH) via GR is necessary for functional photosynthesis and plant growth, we created knockout lines of the homologous enzyme in the model moss Physcomitrella patens. In these viable mutant lines, we found decreasing photosynthetic performance and plant growth with increasing light intensities, whereas ascorbate and zeaxanthin/antheraxanthin levels were elevated. By in vivo monitoring stromal E-GSH dynamics, we show that stromal E-GSH is highly reducing in wild-type and clearly responsive to light, whereas an absence of GR leads to a partial glutathione oxidation, which is not rescued by light. By metabolic labelling, we reveal changing protein abundances in the GR knockout plants, pinpointing the adjustment of chloroplast proteostasis and the induction of plastid protein repair and degradation machineries. Our results indicate that the plastid thioredoxin system is not a functional backup for the plastid glutathione redox systems, whereas GR plays a critical role in maintaining efficient photosynthesis

Single organelle function and organization as estimated from Arabidopsis mitochondrial proteomics

Mitochondria host vital cellular functions, including oxidative phosphorylation and co-factor biosynthesis, which are reflected in their proteome. At the cellular level plant mitochondria are organized into hundreds of discrete functional entities, which undergo dynamic fission and fusion. It is the individual organelle that operates in the living cell, yet biochemical and physiological assessments have exclusively focused on the characteristics of large populations of mitochondria. Here, we explore the protein composition of an individual average plant mitochondrion to deduce principles of functional and structural organisation. We perform proteomics on purified mitochondria from cultured heterotrophic Arabidopsis cells with intensity-based absolute quantification and scale the dataset to the single organelle based on criteria that are justified by experimental evidence and theoretical considerations. We estimate that a total of 1.4 million protein molecules make up a single Arabidopsis mitochondrion on average. Copy numbers of the individual proteins span five orders of magnitude, ranging from >40 000 for Voltage-Dependent Anion Channel 1 to sub-stoichiometric copy numbers, i.e. less than a single copy per single mitochondrion, for several pentatricopeptide repeat proteins that modify mitochondrial transcripts. For our analysis, we consider the physical and chemical constraints of the single organelle and discuss prominent features of mitochondrial architecture, protein biogenesis, oxidative phosphorylation, metabolism, antioxidant defence, genome maintenance, gene expression, and dynamics. While assessing the limitations of our considerations, we exemplify how our understanding of biochemical function and structural organization of plant mitochondria can be connected in order to obtain global and specific insights into how organelles work