Abstract
Plastid transcription plays an important role in plastid differentiation. Proteome analysis of pTAC, plastid transcriptional active chromosome, revealed several plant-specific putative gene regulatory proteins that have no homologue in cyanobacteria, in addition to the bacterial-type RNA polymerase (PEP) subunits. Thus it is likely that plastid transcription is regulated by non-cyanobacterial factors during plastid differentiation. pTAC3 is one of the plant-specific pTAC proteins, and has a sap domain that is involved in DNA binding in eukaryotic matrix attachment region binding proteins. Gel shift assay suggested that the sap domain possesses non-specific DNA binding activity. To examine the role of pTAC3 in plastid differentiation, we isolated a T-DNA insertion mutant of pTAC3. The ptac3 mutant shows an albino phenotype, and a significant decrease in the expression of all PEP-dependent photosynthesis and rRNA genes. These results suggest the possible involvement of pTAC3 in the regulation of plastid gene expression during chloroplast development.
