Institut de Biologie des Plantes - UMR 8618

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• Graham Noctor (Professor, Université Paris sud)
• Caroline Lelarge Trouverie ((IE Université)
• Amna Mhamdi (Post-doc)
• Shengchun Li (PhD student)
• Sylviane Rahantaniaina (PhD student)

RESEARCH THEMES

Context and rationale. Plants are generally sessile organisms and are therefore constrained to withstand environmental fluctuations and to acclimate to them through appropriate perception-response mechanisms. The growth of plants is underpinned by highly energetic redox chemistry in photosynthetic and respiratory pathways. Our increased understanding of the complexity of cellular signalling and control mechanisms includes the growing awareness that redox-dependent signalling is an important interface between the environment and plant function .

Figure 1. Redox components in the detection and transmission of environmental signals Environmental fluctuations, notably stresses, induce changes in cellular redox state that influence or even determine the outcome of the stress. Our goals are to understand how redox components interact with each other and how these interactions influence processes such as cell death or acclimation in response to stress, eg, by impacting on signalling through phytohormone-dependent pathways.

Redox signalling notably involves compounds such as reactive oxygen species (ROS) like H2O2 and the antioxidant and reductant compounds with which these species interact. Together, these molecules form a “redox hub” whose status can influence growth and developmental processes in plants, as well as responses to environmental challenges such as pathogen attack (Foyer and Noctor 2011 Plant Physiol). The primary aims of our lab’s research are (1) to identify how the different components of this redox hub interact during plant responses to fluctuating environmental conditions, and (2) to uncover how specific components of the redox hub operate within the complex web of cellular metabolic signalling pathways. Our approach is one of molecular physiology in which the effects of genetically modulating specific redox components are analyzed using a multi-level integrated approach, with a focus on redox profiling, transcriptomics and metabolomics, as well as cell biology techniques. Because of the incomparable genetic tools available in this plant, our recent studies have been focused on Arabidopsis, but we also work on plants of agronomic importance such as barley and soybean.

Photorespiratory mutants. Photorespiration is an important metabolic pathway that can limit photosynthesis and yield in most plants. During photorespiration, H2O2 is obligatorily produced at high rates in the peroxisomes, where it is metabolized primarily by a specific catalase (Queval et al. 2007 Plant J). Because of the conditional nature of photorespiration, which can be suppressed by growth in certain conditions, mutants deficient in this catalase offer an interesting system in which intracellular H2O2 availability can be triggered in a controllable and inducible fashion, thereby simulating the oxidative component of many environmental stresses (Mhamdi et al. 2010 J Exp Bot). The catalase mutant therefore enables oxidative signals similar to those that occur during environmental fluctuations to be generated conditionally through an endogenous, physiologically relevant pathway

Figure 2 : Catalases as key redox guardians. Plant catalases are encoded by three genes, and the best characterized activity of the encoded proteins is in the metabolism of H2O2 produced in the peroxisomes. Because Arabidopsis CAT2 encodes the major leaf form, mutants in which CAT2 is down-regulated are useful systems to study H2O2 signalling, which can trigger a wide range of defence responses even in the absence of external stress. Source : Mhamdi et al. (2012) Arch Biochem Biophys (in press)

Intracellular oxidative stress in pathogenesis responses. Reactive oxygen species such as H2O2 have been known for many years to play an important role in the responses of plants to invading microorganisms, but the interactions between different subcellular compartments in ROS production during pathogenesis responses are still far from clear. Our studies on the catalase mutant have shown that the response to intracellular oxidative stress is tightly conditioned by growth day length so that lesions are only observed in long days (Queval et al. 2007 ; Queval, Neukermans et al. 2012 Plant Cell Environ). Lesion formation and associated pathogen resistance observed in these conditions can be wholly prevented by genetically blocking salicylic acid (SA) synthesis (Chaouch et al. 2010 Plant Physiol). Thus, oxidative signals originating in the peroxisomes can trigger similar responses to those produced by certain plant pathogens. Signals dependent on NADPH oxidases are well known to play key roles in pathogenesis responses : recently, through a metabolomic analysis of double and single mutants, we have dissected the functional interaction between intracellular redox signals and specific NADPH oxidases during defence responses (Chaouch et al. 2012 Plant J). We have also shown that lesion formation and SA accumulation triggered by intracellular oxidative stress are accompanied by decreases in myo-inositol and can be prevented by exogenously supplying this compound (Chaouch and Noctor 2010 New Phytol).

Pyridine nucleotides. As in almost all organisms, the key players underpinning redox exchange in the soluble phase of plant cells are the pyridine nucleotides, NAD(H) and NADP(H). Their status could impact on ROS availability in plant cells in at least three ways : (1) sufficient amounts of their oxidised forms must be present to prevent excessive conversion of oxygen to ROS by electron transport chains ; (2) their reduced forms can fuel ROS production by NADPH oxidases ; (3) reduced NAD(P) is necessary for maintenance of antioxidant pools such as glutathione. In addition, some studies point to a redox-independent role for NAD(P) in cellular signalling. We are investigating these questions using reverse genetics approaches to target specific components. Earlier studies in our lab showed that metabolic adjustments in the CMSII mutant, which is deficient in mitochondrial complex I and has enhanced stress resistance (Dutilleul et al. 2003 Plant Cell), notably includes increased leaf contents of NAD (Dutilleul et al. 2005 Plant Physiol ; Hager et al. 2010 Planta). Recently, we have reported that targeted increases in NAD by manipulation of the synthetic pathway induce a specific transcriptomic signature that is enriched in pathogenesis-associated genes (Noctor et al. 2011 Adv Bot Res). Because of the key position of NADP(H) in the regulation of redox state, a related ongoing project is investigating the role of specific cytosolic NADP-dependent dehydrogenases in antioxidant homeostasis and defence responses (Mhamdi et al. 2010 Plant Cell Environ). Glutathione. Among its many functions, the tripeptide glutathione is a redox buffer that links NADPH, ROS, and protein thiol/disulphide status. Oxidative stress conditions are known to trigger changes in glutathione status that could play roles in signalling.

Figure 3 : Conditional modulation of glutathione status by intracellular H2O2 in catalase-deficient Arabidopsis mutants. Top, plant phenotypes. Bottom, leaf glutathione contents. White blocks, thiol (reduced) form of glutathione. Red blocks, disulfide (oxidized) form of glutathione that accumulates in response to increased H2O2. Numbers above the bars show % glutathione in the reduced form. When plants are grown in air, the cat2 mutant shows a dwarfed phenotype accompanied by accumulation of GSSG (left). If cat2 is grown at high CO2, where photorespiratory H2O2 production is suppressed, the mutant has the same phenotype and highly reduced glutathione pool as in the wild-type, Col-0 (centre). Transfer of plants grown at high CO2 to air induces accumulation of GSSG within hours and after 4 days glutathione status in cat2 is similar to that observed during growth in air from seed (compare left and right frames) but without the dwarf phenotype (top right). These properties make the cat2 mutant an interesting system in which to study interactions between H2O2 and the glutathione-NADPH system, for example, by introducing specific secondary mutations into the cat2 background. Figure adapted from Mhamdi et al. (2010) J Exp Bot 61, 4197-4220.

Metabolite profiling of the cat2 mutant in conditions of oxidative stress showed that glutathione accumulation is associated with an induction of its amino acid precursors and of genes encoding specific enzymes involved in cysteine synthesis (Queval et al. 2009 Mol Plant). In a subsequent study, we reported the first comprehensive analysis of the differential compartmentalisation of H2O2-triggered glutathione accumulation in leaf mesophyll cells (Queval et al. 2011 Plant Cell Environ). The antioxidant function of glutathione is underpinned by glutathione reductase (GR), for which two genes have been described in plants, with the cytosolic isoform being encoded by GR1. Surprisingly, knockout gr1 mutants show no obvious phenotype. However, using the catalase-deficient cat2 mutant as a tester background for genes that are important in oxidative stress, we reported that GR1 is essential both for maintenance of glutathione status and appropriate signalling through phytohormone pathways when H2O2 availability increases (Mhamdi et al. 2010 Plant Physiol). Knockout gr1 mutants also show enhanced susceptibility when challenged with certain pathogens. An ongoing project is using a direct genetic approach to establish the importance of glutathione status itself in linking H2O2 signals to downstream pathogenesis responses and related phytohormone-dependent pathways.

PUBLICATIONS 2009-2012

Foyer CH, Noctor G (2009) Redox regulation in photosynthetic organisms : signaling, acclimation, and practical implications Antioxidants and Redox Signaling 11, 861-905

Queval G, Thominet D, Vanacker H, Miginiac-Maslow M, Gakière B, Noctor G (2009) H2O2-activated up-regulation of glutathione in Arabidopsis involves induction of genes encoding enzymes involved in cysteine synthesis in the chloroplast. Molecular Plant 2, 344-356

Foyer CH, Bloom AJ, Queval G, Noctor G (2009) Photorespiratory metabolism : genes, mutants, energetics, and redox signaling. Annual Review of Plant Biology 60, 455-484

Frottin F, Espagne C, Traverso JA, Mauve C, Valot B, Lelarge-Trouverie C, Zivy M, Noctor G, Meinnel T, Giglione C (2009) Cotranslational proteolysis dominates glutathione homeostasis for proper growth and development. Plant Cell 21, 3296-3314

Hager J, Pellny T, Mauve C, Lelarge-Trouverie C, Prioul JL, De Paepe R, Foyer CH, Noctor G (2010) Conditional modulation of NAD levels and metabolite profiles in Nicotiana sylvestris by mitochondrial electron transport and carbon/nitrogen supply. Planta 231, 1145-1157

Mhamdi A, Mauve C, Gouia H, Saindrenan P, Hodges M, Noctor G (2010) Cytosolic NADP-dependent isocitrate dehydrogenase contributes to redox homeostasis and the regulation of pathogen responses in Arabidopsis leaves. Plant, Cell & Environment 33, 1112-1123

Mhamdi A, Hager J, Chaouch S, Queval G, Han Y, Taconnat Y, Saindrenan P, Issakidis-Bourguet E, Gouia H, Renou JP, Noctor G (2010) Arabidopsis GLUTATHIONE REDUCTASE 1 is essential for the metabolism of intracellular H2O2 and to enable appropriate gene expression through both salicylic acid and jasmonic acid signaling pathways. Plant Physiology 153, 1144-1160

Simon C, Langlois-Meurinne M, Bellvert F, Garmier M, Massoud K, Chaouch S, Marie A, Bodo B, Noctor G, Saindrenan P (2010) Differential spatial distribution of secondary metabolites in Arabidopsis leaves reacting hypersensitively to Pseudomonas syringae pv. tomato : a strategy for oxidative stress protection. Journal of Experimental Botany 61, 3355-3370

Chaouch S, Queval G, Vanderauwera S, Mhamdi A, Vandorpe M, Langlois-Meurinne M, Van Breusegem F, Saindrenan P, Noctor G (2010) Peroxisomal H2O2 is coupled to biotic defense responses by ICS1 in a daylength-dependent manner. Plant Physiology 153, 1692-1705

Mhamdi A, Queval G, Chaouch S, Vanderauwera S, Van Breusegem F, Noctor G (2010) Catalases in plants : a focus on Arabidopsis mutants as stress-mimic models. Journal of Experimental Botany 61, 4197-4220

Chaouch S, Noctor G (2010) myo-Inositol abolishes salicylic acid-dependent cell death and pathogen defence responses triggered by peroxisomal H2O2. New Phytologist 188, 711-718

Prins A, Mukubi JM, Pellny TK, Verrier P, Beyene G, Lopes MSS, Emami K, Treumann A, Lelarge-Trouverie C, Noctor G, Kunert KG, Kerchev P, Foyer CH (2011) Acclimation to high CO2 in maize is related to water status and dependent on leaf rank. Plant, Cell & Environment 34, 213-231

Foyer CH, Noctor G (2011) Ascorbate and glutathione : the heart of the redox hub. Plant Physiology 155, 2-18

Noctor G, Queval G, Mhamdi A, Chaouch S, Foyer CH (2011) Glutathione.The Arabidopsis Book http://www.bioone.org/doi/full/10.1...

Queval G, Jaillard D, Zechmann B, Noctor G (2011) Increased intracellular H2O2 availability preferentially drives glutathione accumulation in vacuoles and chloroplasts. Plant, Cell & Environment 34, 21-32

Foyer CH, Noctor G, Hodges M (2011) Respiration and nitrogen assimilation : targeting mitochondria-associated metabolism as a means to enhance nitrogen use efficiency. Journal of Experimental Botany 62, 1467-1482

Queval G, Neukermans J, Vanderauwera S, Van Breusegem F, Noctor G (2011) Daylength is a key regulator of transcriptomic responses to both CO2 and H2O2 in Arabidopsis. Plant, Cell & Environment 37, 374-387

Vivancos PD, Driscoll SP, Bulman CA, Ying L, Emami K, Treumann A, Mauve C, Noctor G, Foyer CH (2011) Perturbations of amino acid metabolism associated with glyphosate-dependent inhibition of shikimic acid metabolism affect cellular redox homeostasis and alter the abundance of proteins involved in photosynthesis and photorespiration. Plant Physiology 157, 256-268

Noctor G, Hager, J, Li S (2011) NAD synthesis and its manipulation in plants. Advances in Botanical Research, issue on Biosynthesis of Vitamins in Plants 58, 153-201

Virlouvet L, Jacquemot MP, Gerentes D, Corti H, Bouton S, Gilard F, Valot B, Trouverie J, Tcherkez G, Falque M, Damerval C, Rogowsky P, Perez P, Noctor G, Zivy M, Coursol S (2011) The Zea mays abscisic acid-, stress- and ripening-induced protein ZmASR1 influences branched-chain amino acid biosynthesis and maintains kernel yield under water-limited condition in maize. Plant Physiology 157 : 917-936

Foyer CH, Noctor G (2012) Editorial : Managing the cellular redox hub in photosynthetic organisms. Plant, Cell & Environment 35, 199-201

Noctor G, Mhamdi A, Chaouch S, Han Y, Neukermans J, Queval G, Foyer CH (2012) Glutathione in plants : an integrated overview. Plant, Cell & Environment 35, 454-84

Queval G, Neukermans J, Vanderauwera S, Van Breusegem F, Noctor G (2012) Daylength is a key regulator of transcriptomic responses to both CO2 and H2O2 in Arabidopsis. Plant, Cell & Environment 35, 374-387

Chaouch S, Queval G, Noctor G (2012) AtrbohF is a crucial modulator of defence-associated metabolism and a key actor in the interplay between intracellular oxidative stress and pathogenesis responses in Arabidopsis. The Plant Journal 69, 613-627

Pétriacq P, de Bont L, Hager J, Didierlaurent L, Mauve C, Guérard F, Noctor G, Pelletier S, Renou JP, Tcherkez G, Gakière B (2012) Inducible NAD overproduction in Arabidopsis alters metabolic pools and gene expression correlated with increased salicylate content and resistance to Pst-AvrRpm1. The Plant Journal doi : 10.1111/j.1365-313X.2012.04920.x.

Foyer CH, Neukermans J, Queval G, Noctor G, Harbinson J (2012) Photosynthetic control of electron transport and the regulation of gene expression. Journal of Experimental Botany 63:1637-1661

Kangasjärvi S, Neukermans J, Li S, Aro E-M, Noctor G (2012) Photosynthesis, photorespiration, and light signalling in defence responses. Journal of Experimental Botany 63:1619-1636

Schulz P, Neukermans J, Van Der Kelen K, Mühlenbock P, Van Breusegem F, Noctor G, Teige M, Metzlaff M, Hannah M (2012) Chemical PARP inhibition enhances growth of Arabidopsis and reduces anthocyanin accumulation and the activation of stress protective mechanisms. PLOS one (in press)

Mhamdi A, Noctor G, Baker A (2012) Plant catalases : peroxisomal redox guardians. Archives of Biochemistry and Biophysics (in press)