RNA editing in wheat mitochondria.

C to U transitions in plant mitochondrial mRNA (RNA editing) lead to amino acid changes as well as to the creation of new initiation or termination codons. We established an in vitro system to assay and to dissect the process of wheat mitochondrial mRNA editing. A deamination mechanism explains most easily the observed C to U transitions. Several fractions of organellar protein participate in the editing machinery. Some of these proteins presumably carry the catalytic activity while others are typical RNA binding proteins and may confer specificity to the 'editosome' complex. To investigate the functional properties of protein products synthesized from unedited mRNAs, we constructed transgenic 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 presequence. A significant number of male sterile tobacco plants were obtained suggesting that at least the functional ATP9 protein requires RNA editing. This result suggests a novel approach to obtain artificial male sterile plants by using a physiological effect resulting in CMS which mimics the situation found in many natural populations.