Abstract
It has been hypothesised that there are retrograde signals ("plastid signals") derived from plastids to control nuclear photosynthesis-related gene expression. Although the involvement of tetrapyrrole biosynthesis has been strongly suggested based on the analysis of Arabidopsis gun mutants, the entity of the signal is still obscure. Therefore, we further examined the tetrapyrrole biosynthesis mutants, and found that defects in tetrapyrrole synthesis before ProtoIX does not alter plastid signaling. On the other hand, Fe-branch of tetrapyrrole synthesis is suggested to be involved in plastid signaling, and this is interpreted that the inhibitory effect of chlorophyll synthesis by an accumulated heme in hy1 and hy2 (heme oxygenase and phytochromobilin synthase mutants, respectively). However, it is still vague whether an accumulation of heme or a defect in phytchrome-signaling is the cause of phenotype is not clear. We address this question using phytochrome mutants and transgenic lines that have altered chromophore metabolism. We would also like to present our recent progress on the mutant screening in plastid signaling using FOX-hunting system.
