Our research explores several aspects of the regulation of plant metabolism in response to stress, with a particular emphasis on mitochondrial metabolism. In plants, the process of aging as well as many environmental constraints may lead to the death of leaves. This particular type of cell death is often referred to as leaf senescence and can have a profoundly negative impact on crop yields and post-harvest shelf-life.

Olivier Keech sitting in his office (photo taken by Fredrik Larsson)Photo: Fredrik Larsson

Aim: Leaves are essential plant structures and their well-being is crucial for plant development and survival. When a stress is applied, a plant has two options: try to cope with it or induce senescence and reallocate valuable nutrients towards new, developing or storage organs. A mutual antagonistic relationship can summarize this phenomenon as shown in figure 1. Our aim is to understand how the plant validates senescence over an adaptation strategy in response to stress (Fig. 1). This work mainly covers two aspects: 1) to unveil the communication and signalling mechanisms controlling the induction of leaf senescence and 2) to determine the subsequent metabolic regulation that occurs in response to stress, and ultimately during leaf senescence.

Mutual antagonistic relationship between adaptation and induction of senescence in response to a stress (e.g. nutrient deficiency, light regime, temperatures, pathogene infection, etc).Figure 1: Mutual antagonistic relationship between adaptation and induction of senescence in response to a stress (e.g. nutrient deficiency, light regime, temperatures, pathogene infection, etc).

1. Using dark-induced senescence as a proxy to decipher signalling pathways controlling the induction of leaf senescence

In earlier studies (Keech et al., 2007; Law et al., 2018), we have shown that a leaf from a plant entirely darkened (DP) can survive much longer than an individually-darkened leaf (IDL; Fig. 2), which suggests that upon the right signals, the induction of leaf senescence can be repressed and alternative metabolic strategies conferring extended longevity can occur.

Experimental setup for the two darkening treatments (Weaver and Amasino, 2001; Keech et al., 2007; Law et al., 2018). Figure 2: Experimental setup for the two darkening treatments (Weaver and Amasino, 2001; Keech et al., 2007; Law et al., 2018).

Yet, our current knowledge on the respective metabolic adjustments remains highly fragmented. In 2018, we proposed the following working models (Fig. 3).

Model summarising the different metabolic strategies employed by plants in response to partial or total darkening of the plant. Size and line-weight of the fonts and arrows are proportional to their implication to these metabolic processes. The large arrow behind the leaf in DP conditions depicts the conserved metabolic strategy main-tained between 3 and 6 days of darkening. Abbreviations: AAA - aromatic amino acids, BCAA - branched chain amino acids, Citr - citrate, mETC  - mitochondrial electron trans-port chain, OAA - oxaloacetate, PPP - pentose phosphate pathway, Shik/Chor - shikimate/chorismate, TCA - tricarboxylic acid cycle (Law et al., 2018).B) "Are plants afraid of the dark?" Comic strip by Neil E. Robbins II explaining the content of the publication in a humoristic way. Find the full comic strip here: https://neilercomics.com/2018/05/18/are-plants-afraid-of-the-dark/

Figure 3: A) Model summarising the different metabolic strategies employed by plants in response to partial or total darkening of the plant. Size and line-weight of the fonts and arrows are proportional to their implication to these metabolic processes. The large arrow behind the leaf in DP conditions depicts the conserved metabolic strategy main-tained between 3 and 6 days of darkening. Abbreviations: AAA - aromatic amino acids, BCAA - branched chain amino acids, Citr - citrate, mETC - mitochondrial electron trans-port chain, OAA - oxaloacetate, PPP - pentose phosphate pathway, Shik/Chor - shikimate/chorismate, TCA - tricarboxylic acid cycle (Law et al., 2018); B) "Are plants afraid of the dark?" Comic strip by Neil E. Robbins II explaining the content of the publication in a humoristic way. Find the full comic strip here: https://neilercomics.com/2018/05/18/are-plants-afraid-of-the-dark/

However, in order to challenge these hypotheses, we are currently investigating the metabolic regulations in a set of functional stay-green mutants issued from a genetic screen. This provides us with a much valuable tool to determine how cells can survive prolonged stress conditions.

2. Regulation of metabolism during leaf senescence

In a green leaf, the three energy organelles (peroxisome, mitochondrion and chloroplast) work in synergy to sustain an efficient assimilation of carbon while constantly maintaining the essential functions of the cell. However, when a leaf undergoes senescence (“yellowing”), whole cell-metabolism is drastically modified, and as chloroplasts are rapidly getting impaired, the remaining organelles acquire novel functions, particularly the mitochondrion. In animals, mitochondria have been shown to integrate various signals and to subsequently modulate cell death processes whereas in plants, the contribution of mitochondria in cell death regulation remains unclear, particularly during leaf senescence.

Therefore, we are currently investigating in more detail the role of mitochondria during both developmental (i.e. aging) and stress-induced leaf senescence (Fig. 4).Production of glutamate, reducing equivalents and TCA cycle intermediates from catabolic reactions occurring in the mitochondrion during developmental leaf senescence (Chrobok et al., 2016). Transcriptomic overview of the mitochondrially localised portion of the following metabolic pathways: (I) Lysine degradation, (II) branched chain amino acid degradation, (III) D-2HG metabolism, (IV) Glycine and Alanine metabolism, (V) Urea Cycle and (VI) Proline metabolism. Specific genes of these pathways and their transcript abundance during developmental leaf senescence are illustrated here. Production of reducing equivalents is shown as an arrow with an electron (e-).Figure 4: Production of glutamate, reducing equivalents and TCA cycle intermediates from catabolic reactions occurring in the mitochondrion during developmental leaf senescence (Chrobok et al., 2016). Transcriptomic overview of the mitochondrially localised portion of the following metabolic pathways: (I) Lysine degradation, (II) branched chain amino acid degradation, (III) D-2HG metabolism, (IV) Glycine and Alanine metabolism, (V) Urea Cycle and (VI) Proline metabolism. Specific genes of these pathways and their transcript abundance during developmental leaf senescence are illustrated here. Production of reducing equivalents is shown as an arrow with an electron (e-).


Publication list

  1. Gene atlas of iron-containing proteins in Arabidopsis thaliana
    Plant J. 2021 Jan 10. Epub ahead of print
  2. Iron-sulfur proteins in plant mitochondria: roles and maturation
    J Exp Bot. 2020 Dec 10, Online ahead of print
  3. Siberian larch (Larix sibirica Ledeb.) mitochondrial genome assembled using both short and long nucleotide sequence reads is currently the largest known mitogenome
    BMC Genomics 2020, 21(1):654
  4. Centralization Within Sub-Experiments Enhances the Biological Relevance of Gene Co-expression Networks: A Plant Mitochondrial Case Study
    Front. Plant Sci. 2020, 11:524
  5. Tissue-Specific Isolation of Arabidopsis/plant Mitochondria- IMTACT (Isolation of Mitochondria TAgged in specific Cell Types)
    Plant J. 2020, 103(1):459-473
  6. The mitogenome of Norway spruce and a reappraisal of mitochondrial recombination in plants
    Genome Biol Evol. 2020, 12(1):3586-3598
  7. Functional, Structural and Biochemical Features of Plant Serinyl-Glutathione Transferases
    Front. Plant Sci. 2019, 10:608
  8. Darkened leaves use different metabolic strategies for senescence and survival
    Plant Physiol. 2018; 177 (1):132-150
  9. In Vitro Alkylation Methods for Assessing the Protein Redox State
    Methods Mol Biol. 2017, 1653:51-64
  10. Characterization of a novel β-barrel protein (AtOM47) from the mitochondrial outer membrane of Arabidopsis thaliana
    Journal of Experimental Botany 2016, 67(21):6061-6075
  11. Dissecting the metabolic role of mitochondria during developmental leaf senescence
    Plant Physiol. 2016, 172 (4):2132-2153
  12. Dark-induced leaf senescence: new insights into a complex light-dependent regulatory pathway
    New Phytologist 2016, 212(3):563-570
  13. Mitochondrial uncouplers inhibit clathrin-mediated endocytosis largely through cytoplasmic acidification
    Nature Communications 2016, 7, Article number: 11710
  14. Perspectives for a better understanding of the metabolic integration of photorespiration within a complex plant primary metabolism network
    J Exp Bot. 2016, 67(10):3015-3026
  15. Manipulating photorespiration to increase plant productivity: recent advances and perspectives for crop improvement
    J Exp Bot. 2016, 67(10):2977-2988
  16. Reduced mitochondrial malate dehydrogenase activity has a strong effect on photorespiratory metabolism as revealed by 13C labelling
    J Exp Bot. 2016, 67(10):3123-3135
  17. The redox control of photorespiration: from biochemical and physiological aspects to biotechnological considerations
    Plant Cell Environ. 2017, 40 (4):553-569
  18. The still mysterious roles of cysteine-containing glutathione transferases in plants
    Front. Pharmacol. 2014, 5:192
  19. In response to partial plant shading, the lack of phytochrome A does not directly induce leaf senescence but alters the fine-tuning of chlorophyll biosynthesis
    J. Exp. Bot. 2014, 65(14):4037-4049
  20. The Norway spruce genome sequence and conifer genome evolution
    Nature 2013; 497(7451):579-584
  21. Requirement For The Plastidial Oxidative Pentose Phosphate Pathway For Nitrate Assimilation In Arabidopsis
    The Plant Journal 2013, Online before publication
  22. Fernie AR, Bauwe H, Eisenhut M, Florian A, Hanson DT, Hagemann M, Keech O, Mielewczik M, Nikoloski Z, Peterhänsel C, Roje S, Sage R, Timm S, von Cammerer S, Weber APM, Westhoff P
    Perspectives on plant photorespiratory metabolism.
    Plant Biology 2013; 15(4):748-753
  23. Peterhansel C, Krause K, Braun HP, Espie GS, Fernie AR, Hanson DT, Keech O, Maurino VG, Mielewczik M, Sage RF
    Engineering photorespiration: current state and future possibilities
    Plant Biology 2013; 15(4):754-758
  24. Keech O, Zhou W, Fenske R, Colas des Francs-Small C, Bussell JD, Badger MR, Smith SM
    The genetic dissection of a short term response to low CO2 supports the possibility for peroxide-mediated decarboxylation of photorespiratory intermediates in the peroxisome
    Mol. Plant (2012), online: September 30, 2012.
  25. Brouwer B, Ziolkowska A, Bagard M, Keech O, Gardestrom P
    The impact of light intensity on shade-induced leaf senescence
    Plant, Cell & Environment Jan 2012 35(6):1084-98
  26. Keech O, Pesquet E, Gutierrez L, Ahad A, Bellini C, Smith SM, Gardeström P
    Leaf senescence Is accompanied by an early disruption of the microtubule network in Arabidopsis
    Plant Physiology: 2010 154:1710-1720
  27. Sani M-A, Keech O, Gardeström P, Dufourc EJ, Gröbner G
    Magic-angle phosphorus NMR of functional mitochondria: in situ monitoring of lipid response under apoptotic-like stress
    The FASEB Journal: 2009 23:2872-2878
  28. Keech O, Pesquet E, Ahad A, Askne A, Nordvall D, Vodnala SM, Tuominen H, Hurry V, Dizengremel P, Gardeström P
    The different fates of mitochondria and chloroplasts during dark-induced senescence in Arabidopsis leaves
    Plant, Cell and Environment: 2007 30:1523-1534
  29. Gama F, Keech O, Eymery F, Finkemeier I, Gelhaye E, Gardeström P, Dietz KJ, Rey P, Jacquot J-P, Rouhier N
    The mitochondrial type II peroxiredoxin from poplar
    Physiologia Plantarum: 2007 129:196-206
  30. Keech O, Carcaillet C, Nilsson MC
    Adsorption of allelopathic compounds by wood-derived charcoal: the role of wood porosity
    Plant and Soil: 2005 272:291-300
  31. Rouhier N, Villarejo A, Srivastava M, Gelhaye E, Keech O, Droux M, Finkemeier I, Samuelsson G, Dietz KJ, Jacquot J-P, Wingsle G
    Identification of plant glutaredoxin targets
    Antioxid Redox Signal: 2005 7:919-929
  32. Keech O, Dizengremel P, Gardestrom P
    Preparation of leaf mitochondria from Arabidopsis thaliana
    Physiologia Plantarum: 2005 124:403-409