Retrograde signals from endosymbiotic organelles: a common control principle in eukaryotic cells

Endosymbiotic organelles of eukaryotic cells, the plastids, including chloroplasts and mitochondria, are highly integrated into cellular signalling networks.

plastids and/or mitochondria require extensive organelle-to-nucleus communication in order to establish a coordinated expression of their own genomes with the nuclear genome, which encodes the majority of the components of these organelles.

This goal is achieved by the use of a variety of signals that inform the cell nucleus about the number and developmental status of the organelles and their reaction to changing external environments.

Life on Earth can be subdivided into three different major domains, the Bacteria, the Archaea and the Eukarya [1]. Typically, only the latter (maybe with the exception of some actinomycetes) form complex, multicellular organisms since they possess a number of specific structural and functional properties that are not found in the other two domains. One of the most important features of the Eukarya is their high degree of intracellular compartmentalization, giving rise to a number of membrane-bound structures and organelles with specific biochemical activities. The most prominent is the cell nucleus, which is not present in Bacteria and Archaea. Therefore, these two are often summarized as prokaryotes while the Eukarya are distinguished from them as eukaryotes by having a ‘true nucleus’, the literal meaning of the term [1].

Present plastids and mitochondria are essential compartments of eukaryotic cells and make a major contribution to their structural and functional properties. Despite many species-specific differences in specific properties, a number of common paradigms can be clearly identified, which contributed to the establishment of multicellular organisms. Retrograde signals from the two types of organelles play an important role in cellular responses to developmental and environmental influences. Across all eukaryotic lines, a number of common principles can be identified which most likely represent the common evolutionary constraints imposed regardless of specific effects on the evolution of single species. The establishment of retrograde signalling pathways, therefore, appears to be located at the root of eukaryotic cell evolution.

Still no clue on how the eukaryotic cell could have evolved from the prokaryote.