Elucidation of signal transduction mechanism of tetrapyrrole-based retrograde signaling in plants

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In higher plants, chloroplast biogenesis involves the coordinated expression of the chloroplast and nuclear genomes, requiring information to be sent from the developing chloroplasts to the nucleus and vice versa. This is achieved through so-called retrograde and anterograde signaling pathways, respectively. Currently, the best model to explain the retrograde signaling is that a specific tetrapyrrole molecules generated by chloroplast as a signal to regulate the expression of nuclear genes required for chloroplast development. Although tetrapyrrole is recognized as an organelle-derived signal, the mechanism of transport from organelle to the nucleus and other organelles is still largely unknown. In this research project, signal transduction mechanism of tetrapyrrole-based retrograde signaling in Arabidopsis thaliana has been investigated.During this research, we have succeeded in identifying candidate proteins involved in tetrapyrrole-derived retrograde signaling. It is possible that the identified ABC transporter is involved in transfer of signaling tetrapyrrole metabolites through envelope membrane of plastids. Furthermore, we found that GUN1, which is the most important component of retrograde signaling, directly binds to tetrapyrrole. These insights will significantly proceed our knowledge about the mechanism of retrograde signaling.