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Leister, Dario (2017): Piecing the Puzzle Together: The Central Role of Reactive Oxygen Species and Redox Hubs in Chloroplast Retrograde Signaling. In: Antioxidants & Redox Signaling
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Abstract

Significance: Reactive oxygen species (ROS) and redox regulation are established components of chloroplast-nucleus retrograde signaling. Recent Advances: In recent years, a complex array of putative retrograde signaling molecules and novel signaling pathways have emerged, including various metabolites, chloroplast translation, mobile transcription factors, calcium, and links to the unfolded protein response. This critical mass of information now permits us to fit individual pieces into a larger picture and outline a few important stimuli and pathways. Critical Issues: In this review, we summarize how ROS and redox hubs directly (e.g., via hydrogen peroxide [H2O2]) and indirectly (e.g., by triggering the production of signaling metabolites) regulate chloroplast retrograde signaling. Indeed, evidence is accumulating that most of the presumptive signaling metabolites so far identified are produced directly by ROS (such as beta-cyclocitral) or indirectly by redox- or ROS-mediated regulation of key enzymes in metabolic pathways, ultimately leading to the accumulation of certain precursors (e.g., methylerythritol cyclodiphosphate and 3-phosphoadenosine 5-phosphate) with signal function. Of the ROS generated in the chloroplast, only H2O2 is likely to leave the organelle, and recent results suggest that efficient and specific transfer of information via H2O2 occurs through physical association of chloroplasts with the nucleus. Future Directions: The impact of ROS and redox regulation on chloroplast-nucleus communication is even greater than previously thought, and it can be expected that further instances of control of retrograde signaling by ROS/redox regulation will be revealed in future, perhaps including the basis for the enigmatic GUN response and translation-dependent signals. Antioxid. Redox Signal. 00, 000-000.