Abstract
Nuclear-encoded genes related to the plastid-structure/function (e.g. Lhcb, RbcS) were coordinately regulated with the functional status of plastids. An unknown signal, called "plastid signal", has been hypothesized for this regulatory mechanism. Analysis of gun mutants that have defects in this signaling has revealed the involvement of the tetrapyrrole intermediates (MgProtoIX) as a signaling factor. However, the accumulation of MgProtoXI and MgProtoIXMe in chlM and crd1 mutants respectively does not repress Lhcb expression. This suggests that MgProtoIX(Me) level does not simply account for the regulation of Lhcb.
MgProtoIX synthesis is catalyzed by Mg-chelatase which is a multi-protein complex consists of ChlH(Gun5)-ChlD-ChlI and Gun4. Recently Gun5 is reported to function as the abscisic acid (ABA) receptor. Detailed analysis of plastid-signal and ABA-related phenotype of Mg-chelatase mutants and other tetrapyrrole mutants will be reported. We will also present the characterization of newly isolated gun mutants.
