MULTIPLE INDEPENDENT LOSSES OF THE RPOC1 INTRON IN ANGIOSPERM CHLOROPLAST DNAS

Previous studies have shown that in Marchantia, black pine, and the va st majority of angiosperms examined to date, the chloroplast gene rpoC 1 is interrupted by an intron (of about 750 base Fairs), but that in t he grasses and one of three subfamilies of cacti (Cactoideae) this int ron has been lost. DNA's of the complete rpoC1 intron region and porti ons of the flanking exon regions from 107 species (representing 54 fam ilies) of angiosperms were amplified with the polymerase chain reactio n (PCR) in order to uncover other instances of intron loss. In additio n to grass and Cactoideae chloroplast DNA's, we report that the rpoC1 intron is missing from the chloroplast genomes of Scaeoola and Goodeni a (the only two representatives of Goodeniaceae examined), four of ten species of Passiflora (Passifloraceae), two of four genera of Aizoace ae (Delosperma and Faucaria but not Monilaria or Tetragonia), and one of the eight taxa of Medicago examined (M. suffruticosa subsp. leiocar pa; Fabaceae). Mirroring other instances of intron loss from the chlor oplast genome, sequence analysis reveals that, for these bra, the rpoC 1 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 p osition in the gene. Parsimony analyses of partial exon and intron rpo C1 nucleotide sequences reveal that the latter, owing to considerable conservation of secondary structure in that region of the intron seque nced, can supply useful characters for phylogenetic analysis at high t axonomic levels.