Retrograde Signalling

Plastids are organelles typical for plant cells. They are a metabolic and genetic compartment that is involved in most aspects of the life of a plant. Plastids were acquired by plants via endosymbiosis of a photosynthetically active prokaryotic ancestor. Establishment of this endosymbiosis required communication between the endosymbiont and the nucleus of the host cell. During evolution a complex network evolved that embedded development and function of the new organelle into that of the cell. Today the nucleus controls most functions of plastids by providing the essential proteins. However, there exists a backward flow of information from the plastid to the nucleus. This “retrograde” signalling represents a feedback control reporting the functional state of the organelle to the nucleus. By this means extensive communication between the two compartments is established. This helps the plant to perceive and respond properly to varying environmental influences and to developmental signals at the cellular level. Recent observations have extended our understanding of retrograde signalling. Models are presented that provide an overview of the different known pathways.