Retrograde signaling in plants: from simple to complex scenarios

Plant Molecular Biology (Botany), Department Biology I, Ludwig Maximilians University, Munich, Germany.
Frontiers in Plant Science (Impact Factor: 3.95). 06/2012; 3:135. DOI: 10.3389/fpls.2012.00135
Source: PubMed

ABSTRACT The concept of retrograde signaling posits that signals originating from chloroplasts or mitochondria modulate the expression of nuclear genes. A popular scenario assumes that signaling factors are generated in, and exported from the organelles, then traverse the cytosol, and act in the nucleus. In this scenario, which is probably over-simplistic, it is tacitly assumed that the signal is transferred by passive diffusion and consequently that changes in nuclear gene expression (NGE) directly reflect changes in the total cellular abundance of putative retrograde signaling factors. Here, this notion is critically discussed, in particular in light of an alternative scenario in which a signaling factor is actively exported from the organelle. In this scenario, NGE can be altered without altering the total concentration of the signaling molecule in the cell as a whole. Moreover, the active transport scenario would include an additional level of complexity, because the rate of the export of the signaling molecule has to be controlled by another signal, which might be considered as the real retrograde signal. Additional alternative scenarios for retrograde signaling pathways are presented, in which the signaling molecules generated in the organelle and the factors that trigger NGE are not necessarily identical. Finally, the diverse consequences of signal integration within the organelle or at the level of NGE are discussed. Overall, regulation of NGE at the nuclear level by independent retrograde signals appears to allow for more complex regulation of NGE than signal integration within the organelle.

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    • "This phenomenon is called retrograde signaling. This retrograde signaling has been extensively studied for chloroplast (Chan et al., 2010; Leister, 2012) but the pathway(s) originating from mitochondria remain(s) unclear (Schwarzlander and Finkemeier, 2013). "
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    • "Shunting electrons through this pathway is important in energy-rich plants cells for primary and secondary metabolism, as well as for oxidation of excess carbohydrate (Rasmusson and Wallström, 2010). The expression of AOX and type II NDH, both of nuclear encoding, is increased during ETC inhibition by mitochondria to nucleus signaling (Van Aken et al., 2009a; Hartl and Finkemeier, 2012; Leister, 2012). In this process, organellar redox state and ROS metabolism have been poproposed as sources for retrograde signals which could trigger gene expression responses and provide a metabolic flexibility which, during stress conditions, play an important role in the acclimation of plants (Rhoads and Subbaiah, 2007; Woodson and Chory, 2008) "
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