A PROMISCUOUS CHLOROPLAST DNA FRAGMENT IS TRANSCRIBED IN PLANT-MITOCHONDRIA BUT THE ENCODED RNA IS NOT EDITED

The RNA editing processes in chloroplasts and mitochondria of higher p lants show several similarities which are suggestive of common compone nts and/or biochemical steps between the two plant organelles. The exi stence of various promiscuous DNA fragments of chloroplast origin in p lant mitochondrial genomes allowed us to test the possibility that chl oroplast sequences are also edited in mitochondria. An rpoB fragment t ransferred from chloroplasts to mitochondria in rice was chosen as it contains several editing sites, two of which match sequence motifs sur rounding even non-homologous editing sites in both chloroplast and mit ochondrial transcripts. Rice chloroplast and mitochondrial rpoB DNA an d cDNA sequences were selectively amplified and the editing status of the cDNA sequences was determined. Three of the four potential rpoB ed iting sites previously detected in maize were found to be edited in th e rice chloroplast rpoB transcript, whereas the fourth was found to re main unedited. In mitochondria, however, all four editing sites remain unmodified at the cDNA level. This indicates that the editing process es of higher plant mitochondria and chloroplasts are not identical and that organelle-specific factors are required for eliciting the respec tive editing events.