The paper:
S. Koussevitzky et al., "Signals from chloroplasts converge to regulate nuclear gene expression," Science, 316:715–9, 2007. (Cited in 58 papers)
The finding:
Joanne Chory, a Salk Institute molecular biologist, used Arabidopsis thaliana mutant screens to identify two key molecular players in the communications between chloroplasts and plant cell nuclei: GUN1, a protein found in chloroplasts that regulates RNA molecules, and ABI4, a nuclear transcription factor. The findings indicated that the few known chloroplast-to-nucleus signals converge on ABI4 and are integrated by GUN1 within the organelle and not in the cytoplasm or nucleus. "That was a big conceptual leap," Chory says.
The significance:
A robust understanding of retrograde signaling—where chloroplasts alter the expression of nuclear genes that encode chloroplast-bound proteins—may help biologists reconstruct cellular endosymbiosis. "How did these organelles evolve communication?" asks Peter McCourt, a University of Toronto plant biologist. "That's a very big, interesting question to all biologists."
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