THE PEPEROMIA MITOCHONDRIAL COXI GROUP-I INTRON - TIMING OF HORIZONTAL TRANSFER AND SUBSEQUENT EVOLUTION OF THE INTRON

The Peperomia polybotrya cox1 gene intron is the only currently report ed group I intron in a vascular plant mitochondrial genome and it like ly originated by horizontal transfer from a fungal donor. We provide a clearer picture of the horizontal transfer and a portrayal of the evo lution of the group I intron since it was gained by the Peperomia mito chondrial genome. The intron was transferred recently in terms of plan t evolution, being restricted to the single genus Peperomia among the order Piperales. Additional support is presented for the suggestion th at a recombination/repair mechanism was used by the intron for integra tion into the Peperomia mitochondrial genome, as a perfect 1:1 corresp ondence exists between the intron's presence in a species and the pres ence of divergent nucleotide markers flanking the intron insertion sit e. Sequencing of cox1 introns from additional Peperomia species reveal ed that several mutations have occurred in the intron since the horizo ntal transfer, but sequence alterations have not caused frameshifts or created stop codons in the intronic open reading frame. In addition, two cox1 pseudogenes in Peperomia cubensis were discovered that lack a large region of cox1 exon 2 and contain a truncated version of the gr oup I intron that likely cannot be spliced out.