STUDIES ON THE EFFECTS OF NUCLEAR BACKGROUND AND TISSUE-SPECIFICITY ON RNA EDITING OF THE MITOCHONDRIAL ATP SYNTHASE SUBUNIT-ALPHA, SUBUNIT-6 AND SUBUNIT-9 IN FERTILE AND CYTOPLASMIC MALE-STERILE (CMS) WHEAT

RNA editing occurs in transcripts encoded by the mitochondrial genome in all major groups of land plants and is characterised by C-to-U edit ing. When editing occurs, the amino acid is usually altered because th e nucleotide modification is generally in the first or second position and the amino acid change improves the conservation of the predicted protein as compared with other organisms. In order to assess the effec t of the nuclear background and tissue specificity of the RNA editing, we have analysed the RNA editing of the transcripts encoding for the mitochondrial ATPsynthase subunits atp alpha, atp6, and atp9 in euplas mic and alloplasmic cytoplasmic male-sterile (CMS) wheat lines. The ed iting of atp alpha was detected in 6 codons. Although partially edited transcripts were found in all the cytoplasms, a larger number of part ially edited clones were present in the CMS cytoplasm. The RNA editing of atp6 occurred in 12 codons, and whereas in the euplasmic Triticum timopheevi all the clones were fully edited, in the CMS line 17% of th e clones were only partially edited, suggesting an effect of the nucle ar background on RNA editing efficiency. In atp9 transcripts, 8 codons were modified by RNA editing. When the RNA editing of the atp9 transc ripts extracted from various tissues was compared, only fully edited c lones were detected in embryos, roots, shoots, and anthers in the eupl asmic wheat lines, whereas in the transcripts obtained from the CMS li ne, 19% of the clones were partially edited. This study reveals that R NA editing efficiency can be affected by the tissue and nuclear backgr ound. The mechanism by which incomplete and complete edited transcript s accumulate may indicate a link between the transcription kinetics an d RNA editing which can be affected by nuclear background and tissue s pecificity.