The aims of the conference were

• to enable a high international visibility of the DFG Research Unit 804 ‘Retrograde Signaling in Plants’ [2]
• to place the scientific topics of the Research Unit into an international context and
• to intensify the international cooperation and exchange of co-workers and students as well as scientific opinions.

More than 100 scientists, national and international experts as well as young researchers at the beginning of their scientific careers, attended the meeting which was organized by the Research Unit and held in October 1-3, 2009, in the Harnack-House of the Max-Planck-Society in Berlin.

Unpublished Data on Plastid and Mitochondrial Signaling

Oral and poster presentations documented the high impact of recent studies of retrograde signaling pathways on the research area of plant cell biology. Leading experts with interdisciplinary expertise in Genetics, Biochemistry, Physiology and Bioinformatics reported novel, mainly unpublished data and contributed to a well-acknowledged view on the state of the art on plastid and mitochondrial signaling, while young scientists took the opportunity to present their results to the international attendees and to contribute to an encouraging and stimulating discussion.

Regulatory Cross-Talk

In fact, the conference was held in a period of growing interest in the research subject of retrograde signaling. In the last years a number of reports were published by partners of the Research Unit and other scientists that indicate the scientific significance and attraction of retrograde signals emanating from plastids. It was generally acknowledged that parallel synthesis of stoichiometric amounts of proteins for the coordinated and accurate assembly of protein complexes by different genomes requires an intracellular regulatory cross-talk. Plastid-derived signaling decisively contributes to cellular homeostasis and controlled balance of nuclear gene expression in response to plastid biogenesis and metabolic activities.

Where do Downstream Responses Result from?

At present the identification and characterization of retrograde signals of different nature provide a complex picture of the regulatory and physiological properties of intracellular signaling pathways. It became obvious that diverse signaling pathways from chloroplasts to the nucleus are emitted from different signaling molecules and operate at different functional and developmental states of plants. The current discussion is ongoing whether the downstream responses are the result of combined and cumulative signaling pathways of adverse, inconvenient and stimulatory signals and whether the complex signaling pattern will lead to convergence of expression control.

Pressure to Evolve the Transfer of Information

Another finding was that retrograde signaling is involved in most, if not all developmental and physiological aspects of plants (cell division, stress response, leaf morphology) indicating the enormous evolutionary pressure on the generation of strategies to transfer information among the genome-harboring organelles. As one of the most challenging question concerns the transmembrane communication between signal emission in plastids and response reactions in the nucleus, metabolites that normally reflect the physiological state of chloroplast metabolic pathways, could potentially contribute to retrograde signaling. Finally, exploring many signaling mutants indicated that a clear distinction between cause and consequence of changes in the cellular response is only possible with experimental approaches that allow a time-resolved assessment of early and inducible signaling events and help to distinguish between primary and secondary effects of signal emission in plastids.

Thanks

In conclusion, the organizers are thankful for the financial support by German Science Foundation (Deutsche Forschungsgemeinschaft, DFG) and other sponsors like the German Botanical Society that allowed the performance of an inspiring and productive international scientific conference. Thanks to all attendees who made this conference a successful event.

Berlin, May 17th 2010, Professor Dr. Bernhard Grimm