A MITOCHONDRIAL SUB-STOICHIOMETRIC ORF87-NAD3-NAD1 EXONA CO-TRANSCRIPTION UNIT PRESENT IN SOLANACEAE WAS AMPLIFIED IN THE GENUS NICOTIANA

Unlike other plant species, two copies of nad3 are present in Nicotian a sylvestris mitochondria. Both are localized downstream from an open reading frame (orf87), and are associated with either rps12 or the fir st exon of the nad1 gene. The orf87-nad3-nad1/A cluster is present in normal stoichiometry in Nicotiana tomentosiformis, and is sub-stoichio metric in other Solanaceae, revealing recent amplification in the genu s Nicotiana. It is suggested from sequence analysis that this cluster originated in an homologous recombination event that involved the nad3 -rps12 intergenic region and the upstream region of an ancestral nad1 gene. Transcription patterns and RT-PCR showed that orf87-nad3-rps12 a dn orf87-nad3-nad1/A clusters are both co-transcription units.