Multiple independent losses of the rpoC1 intron in angiosperm chloroplast DNA's

Previous studies have shown that in Marchantia, black pine, and the vast majority of angiosperms examined to date, the chloroplast gene rpoC1 is interrupted by an intron (of about 750 base pairs), but that in the grasses and one of three subfamilies of cacti (Cactoideae) this intron has been lost. DNA's of the complete rpoC1 intron region and portions of the flanking exon regions from 107 species (representing 54 families) of angiosperms were amplified with the polymerase chain reaction (PCR) in order to uncover other instances of intron loss. In addition to grass and Cactoideae chloroplast DNA's, we report that the rpoC1 intron is missing from the chloroplast genomes of Scaevola and Goodenia (the only two representatives of Goodeniaceae examined), four of ten species of Passiflora (Passifloraceae), two of four genera of Aizoaceae (Delosperma and Faucaria but not Monilaria or Tetragonia), and one of the eight taxa of Medicago examined (M. suffruticosa subsp. Iciocarpa; Fabaceae). Mirroring other instances of intron loss from the chloroplast genome, sequence analysis reveals that, for these taxa, the rpoC1 gene has undergone a precise deletion of the intron. For those taxa with the intron, minimal size variation is apparent within the region and, in all taxa investigated, the intron lies in precisely the same position in the gene. Parsimony analyses of partial exon and intron rpoC1 nucleotide sequences reveal that the latter, owing to considerable conservation of secondary stricture in that region of the intron sequenced, can supply useful characters for phylogenetic analysis at high taxonomic levels.