Abstract
Chloroplasts originated from photosynthetic cyanobacterium subsequent to endosymbiotic event. During evolution, most of the cyanobacterial genes were transferred to the host nucleus. Therefore, the precise expression of specific sets of nuclear genes and protein import into plastid are essential for chloroplast biogenesis. One possible cellular mechanism that coordinates these two essential processes is retrograde signaling from plastids to the nucleus. However the molecular mechanisms underlying this inter-organelle signaling remains to be characterized. Down-regulation of photosynthesis-associated genes has been observed in ppi2 (plastid protein import2) mutant lacking the plastid protein import apparatus. Genetic studies revealed that the coordination of plastid protein import and the nuclear gene expression is independent of known signaling components. Instead, it may involve the transcription factor AtGLK1. Overexpression of AtGLK1 in the ppi2 mutant partially restores both photosynthesis-associated gene expression and chlorophyll accumulation. We will discuss the role of AtGLK1 in plastid signaling pathway.
