The present project is focused on analyzing the biological activity of singlet oxygen (1O2). 1O2 is generated mainly photochemically by photosensitization reactions that are the basis for photo- oxidative tissue damage in humans suffering from porphyria and that have been exploited for photodynamic therapies of various benign and malignant diseases. 1O2 has been largely considered to be detrimental to cells due to its high reactivity and potential toxicity. However, recent data suggest that 1O2 may also be perceived as a signal. So far two major obstacles have hampered the analysis of the biological activity of 1O2. First, in cells under stress several other chemically distinct ROS are generated simultaneously, thus making it very difficult to link a particular cellular response to 1O2. Second, it is difficult to define criteria that may be used to distinguish between the cytotoxicity and the signaling role of this ROS. These problems have been alleviated in the present research project by using the conditional flu mutant of Arabidopsis. In the dark the flu mutant accumulates protochlorophyllide, a potent photosensitizer that upon illumination generates 1O2. By varying the length of the dark period one can modulate noninvasively the level of the photosensitizer and define conditions that minimize the cytotoxicity of 1O2 and endorse its signaling. The genetic basis of 1O2- signaling is revealed by the executer1 mutation that is sufficient to abrogate 1O2-mediated stress responses. These responses largely depend on differentially regulated gene expression. Among the genes that are up-regulated right after the release of 1O2, those encoding transcription factors are clearly overrepresented, implicating an as yet largely unexplored transcriptional regulatory network with triggering 1O2-mediated responses. Regulatory modules will be described consisting of primary 1O2-responsive transcription factors and their target genes that play a key role in transforming 1O2- derived signals into 1O2-dependent physiological changes. These responses range from stress acclimation and modifying disease resistance to the initiation of programmed cell death and committing suicide. We will try to understand how a seemingly simple initial event, the release of singlet oxygen, gives rise to the genetically controlled activation of such diverse responses.

Public Health Relevance

Increased levels of chemically distinct reactive oxygen species (ROS) in humans have been associated with various stress symptoms, cancer, cell death, ageing and age-related pathologies such as stroke, neurodegeneration and cardiovascular diseases. Understanding the different roles of each of these ROS during the emergence of such disorders would greatly impact the design of new remedies and treatments. In the present work one of these ROS, singlet oxygen, that formerly had been considered to affect cells primarily by causing oxidative damage, will be analyzed under conditions that minimize its cytotoxicity and reveal the genetic basis of its signaling role.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Cellular Signaling and Regulatory Systems Study Section (CSRS)
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Maas, Stefan
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Boyce Thompson Institute for Plant Research
United States
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Wang, Liangsheng; Kim, Chanhong; Xu, Xia et al. (2016) Singlet oxygen- and EXECUTER1-mediated signaling is initiated in grana margins and depends on the protease FtsH2. Proc Natl Acad Sci U S A 113:E3792-800
Chen, Shiguo; Kim, Chanhong; Lee, Je Min et al. (2015) Blocking the QB-binding site of photosystem II by tenuazonic acid, a non-host-specific toxin of Alternaria alternata, activates singlet oxygen-mediated and EXECUTER-dependent signalling in Arabidopsis. Plant Cell Environ 38:1069-80
Zhang, Shengrui; Apel, Klaus; Kim, Chanhong (2014) Singlet oxygen-mediated and EXECUTER-dependent signalling and acclimation of Arabidopsis thaliana exposed to light stress. Philos Trans R Soc Lond B Biol Sci 369:20130227
Kim, Chanhong; Apel, Klaus (2013) 1O2-mediated and EXECUTER-dependent retrograde plastid-to-nucleus signaling in norflurazon-treated seedlings of Arabidopsis thaliana. Mol Plant 6:1580-91
Kim, Chanhong; Apel, Klaus (2013) Singlet oxygen-mediated signaling in plants: moving from flu to wild type reveals an increasing complexity. Photosynth Res 116:455-64
Šimková, Klára; Kim, Chanhong; Gacek, Katarzyna et al. (2012) The chloroplast division mutant caa33 of Arabidopsis thaliana reveals the crucial impact of chloroplast homeostasis on stress acclimation and retrograde plastid-to-nucleus signaling. Plant J 69:701-12
Simkova, Klara; Moreau, Fanny; Pawlak, Piotr et al. (2012) Integration of stress-related and reactive oxygen species-mediated signals by Topoisomerase VI in Arabidopsis thaliana. Proc Natl Acad Sci U S A 109:16360-5
Kim, Chanhong; Meskauskiene, Rasa; Zhang, Shengrui et al. (2012) Chloroplasts of Arabidopsis are the source and a primary target of a plant-specific programmed cell death signaling pathway. Plant Cell 24:3026-39