Tetrapyrrole-mediated signaling
Chlorophyll is the most abundant pigment in chloroplasts. Since chlorophyll is a strong photosensitizer with a highly destructive capacity, its synthesis must be tightly controlled in close association with synthesis and assembly of light harvesting complexes and reaction centers. The tetrapyrrole biosynthesis pathway is subject to an intricate feedback control and modulation of the initial steps of the Mg branch towards chlorophyll biosynthesis has been demonstrated to elicit plastid-to-nucleus signaling for coordination of nuclear gene expression in response to the physiological and developmental state of the plastid tetrapyrrole metabolism. However, the mode of signal transmission including the identity of signaling components and of the actual messenger molecule(s) remain controversial and require further experimental clarification.