TISSUE-SPECIFIC AND STAGE-SPECIFIC MODULATION OF RNA EDITING OF THE PSBF AND PSBL TRANSCRIPT FROM SPINACH PLASTIDS - A NEW REGULATORY MECHANISM

The psbE operon of spinach chloroplasts, which includes the genes psbE , psbF, psbL and psbJ, encodes two RNA editing sites. One site corresp onds to the initiation codon of the psbL transcript, as has been descr ibed earlier for the homologous transcript from tobacco, while at a se cond editing site, newly reported here, an internal phenylalanine codo n of the psbF transcript is restored. Both these sites were investigat ed with respect to the extent of editing in spinach plastids at variou s developmental stages. The apparent existence of only completely edit ed transcripts in etioplasts and chloroplasts, indicates that light-in duced processes are not acting as determinants in eliciting the editin g process. Reduced editing is, however, observed in the psbF and psbL transcript from seeds and roots. This finding suggests that the RNA ed iting process is differentially down-regulated in leucoplasts and prop lastids and that editing may, therefore, function as a regulatory devi ce in plastid gene expression.