Analysis of singlet oxygen-mediated chloroplast-nucleus signaling in Arabidopsis

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Reactive oxygen species (ROS) emerged as important signals during plant stress responses. Depending on their concentration and intracellular localization each ROS may cause oxidative damage or initiate signaling. However, their mode of action is poorly understood and elucidating the precise signaling roles of each ROS faces the problem that distinct ROS are produced simultaneously. To overcome these restraints I will use the conditional flu mutant of Arabidopsis as an experimental system that allows to dissect the complexity of ROS signaling and to specifically investigate the biological activity of one particular ROS, singlet oxygen (1O2). 1O2 signaling in flu depends on the activity of the EXECUTER1 (EX1) protein. The site of 1O2 production and the localization of EX1 are within the chloroplast. This proximity suggests that the impact of EX1 on 1O2 signaling is likely to occur shortly after or during the release of 1O2. I will characterize EX1 and determine its role during initiation of 1O2 signaling. This has not yet been analyzed in any organism known to generate 1O2. This objective is expected to reveal insights into how a highly reactive ROS may initiate signaling rather than oxidative damage. Among up-regulated genes 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. I 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.