Movement of endosymbiotic organelles

Mitochondria and chloroplasts are both of endosymbiotic origin. Upon symbiosis the ancestral bacteria had to be incorporated into the regulatory cellular network. A long known phenomenon is thereby the alteration of the positioning of the organelles in response to extra- and intracellular stimuli. For chloroplasts, the repositioning is a response to light intensity changes in order to optimize the photosynthetic process. Mitochondria movement ensures a positioning of the organelle close to the place where its function is required, e.g. in metabolic pathways, apoptosis, regulation of cytosolic calcium levels and ATP production. Even though the morphological description of the movement was circumstantiated decades ago, only recent research gave some insights into the molecular concepts behind the movement of organelles and its regulation. Mitochondrial movement is influenced for instance by calcium but also by small molecules like lysophosphatidic acid or metals like zinc. In turn, chloroplasts move in response to light. The light quality giving the impulse for movement depends on the plants investigated. As for mitochondria, calcium is an important second messenger for that process. The organelle movement is achieved by actin or tubulin. The recent discovery of proteins involved in the modulation of the movement like milton and miro in mitochondria or phot1 and phot2 and the organelle localized protein chup1, possibly facilitating the cytoskeleton contact, marked a new area of understanding of the process. This review will focus on a comprehensive overview on recent discoveries of the regulatory components.