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 1150

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 fig 1. Our aim is to understand how the plant validates senescence over an adaptation strategy in response to stress. This work mainly covers two aspects: 1) to unveil the communication and signalling mechanisms controlling the induction of leaf senescence and 2) to characterize the metabolic regulation that occurrs in response to stress and during leaf senescence.

Figures research profile cropped 1Figure 1. Mutual antagonistic relationship between adaptation and induction of senescence in response to a stress.

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

An individually-darkened leaf (IDL) for 6 days will undergo an accelerated senescence, whereas leaves from a plant entirely darkened (DP) for the same period of time will exhibit a sustained maintenance of their physiological functions and a subsequent repression of the process of senescence (Fig 2).
Figures research profile cropped 2Figure 2. Experimental setup for the two darkening treatments (Weaver and Amasino 2001; Keech et al 2007; Keech et al 2010).
Great differences between transcriptomes and metabolomes of IDL and DP are observed, and highlight the different metabolic strategies between the two darkening treatment (Fig 3).

Figures research profile cropped 3Figure 3. Visualization of transcript and metabolic variations in IDL and DP during a time course from 0 to 6 days. At the transcriptomic level, (A) 3D PCA and (B) 2D PCA highlight the progressive separation of the transcriptomes during the two darkening treatments. At the metabolic level, (A) PCA and (B) a supervised method OPLS-DA (Bylesjö et al 2006) show primarily the distinct metabolic profile between light and darkened samples, and secondly the progressive separation of the metabolic profiles between the two darkening treatments, over the duration of the time course

In order to identify the key players involved in the induction of senescence, we undertook a genetic screen allowing isolation of functional stay-green mutants. We are currently unveiling the function of these mutants.

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 details the role of mitochondria during natural leaf senescence (i.e. aging).Figures research profile cropped 4Figure 4. Overview of the mitochondrial transcript expression during leaf senescence. We are particularly interested in unknown genes which encode products predicted to be targeted to mitochondria (unknowns).

Publications list

  1. Darkened leaves use different metabolic strategies for senescence and survival
    Plant Physiol. 2018; 177 (1):132-150
  2. In Vitro Alkylation Methods for Assessing the Protein Redox State
    Methods Mol Biol. 2017, 1653:51-64
  3. 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
  4. Dissecting the metabolic role of mitochondria during developmental leaf senescence
    Plant Physiol. 2016, 172 (4):2132-2153
  5. Dark-induced leaf senescence: new insights into a complex light-dependent regulatory pathway
    New Phytologist 2016, 212(3):563-570
  6. Mitochondrial uncouplers inhibit clathrin-mediated endocytosis largely through cytoplasmic acidification
    Nature Communications 7, Article number: 11710
  7. 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
  8. Manipulating photorespiration to increase plant productivity: recent advances and perspectives for crop improvement
    J Exp Bot. 2016, 67(10):2977-2988
  9. 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
  10. The redox control of photorespiration: from biochemical and physiological aspects to biotechnological considerations
    Plant Cell Environ. 2017, 40 (4):553-569
  11. The still mysterious roles of cysteine-containing glutathione transferases in plants
    Front. Pharmacol. 2014, 5:192
  12. 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

  13. The Norway spruce genome sequence and conifer genome evolution
    Nature 2013; 497(7451):579-584
  14. Requirement For The Plastidial Oxidative Pentose Phosphate Pathway For Nitrate Assimilation In Arabidopsis
    The Plant Journal 2013, Online before publication
  15. 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
  16. 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
  17. 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.
  18. 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
  19. 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
  20. 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
  21. 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
  22. 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
  23. 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
  24. 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
  25. Keech O, Dizengremel P, Gardestrom P
    Preparation of leaf mitochondria from Arabidopsis thaliana
    Physiologia Plantarum: 2005 124:403-409