Heterologous, splicing-dependent RNA editing in chloroplasts: allotetraploidy provides trans-factors

RNA editing is unique among post-transcriptional processes in plastids, as it exhibits extraordinary phylogenetic dynamics leading to species-specific editing site patterns. The evolutionary loss of a site is considered to en tail the loss of the corresponding nuclear-encoded site-specific factor, wh ich prevents the editing of foreign, i.e. heterologous, sites. We investiga ted the editing of short 'spliced' and 'unspliced' ndhA gene fragments from spinach in Nicotiana tabacum (tobacco) in vivo using biolistic transformat ion. Surprisingly, it turned out that the spinach site is edited in the het erologous nuclear background. Furthermore, only exon-exon fusions were edit ed, whereas intron-containing messages remained unprocessed. A homologue of the spinach site was found to be present and edited in Nicotiana tomentosi formis, representing the paternal parent, but absent from Nicotiana sylvest ris, representing the maternal parent of tobacco. Our data show that: (i) t he cis-determinants for ndhA editing are split by an intron; (ii) the editi ng capacity cannot be deduced from editing sites; and (iii) allopolyploidiz ation can increase the editing capacity, which implies that it can influenc e speciation processes in evolution.