RNA EDITING IN WHEAT MITOCHONDRIA

C to U transitions in plant mitochondrial mRNA (RNA editing) lead to a mino acid changes as well as to the creation of new initiation or term ination codons. We established an in vitro system to assay and to diss ect the process of wheat mitochondrial mRNA editing. A deamination mec hanism explains most easily the observed C to U transitions. Several f ractions of organellar protein participate in the editing machinery. S ome of these proteins presumably carry the catalytic activity while ot hers are typical RNA binding proteins and may confer specificity to th e 'editosome' complex. To investigate the functional properties of pro tein products synthesized from unedited mRNAs, we constructed transgen ic tobacco plants carrying an unedited gene coding for subunit 9 (ATP9 ) of the ATP synthase complex. The nuclear encoded 'unedited' protein product is targeted to the mitochondria with a heterologous presequenc e. A significant number of male sterile tobacco plants were obtained s uggesting that at least the functional ATP9 protein requires RNA editi ng. This result suggests a novel approach to obtain artificial male st erile plants by using a physiological effect resulting in CMS which mi mics the situation found in many natural populations.