Loss of Chloroplast trnLUAA Intron in Two Species of Hedysarum (Fabaceae): Evolutionary Implications

Previous studies have indicated that in all land plants examined to date, the chloroplast gene trnLUAA isinterrupted by a single group I intron ranging from 250 to over 1400 bp. The parasitic Epifagus virginiana haslost, however, the entire gene. We report that the intron is missing from the chloroplast genome of twoarctic species of the legume genus Hedysarum (H. alpinum, H. boreale). DNA sequencing of the trnL geneand trnL-trnF intergenic spacer (trnL-F), as well as portion of trnF exon in these species confirms theabsence of trnL intron and shows that it has been deleted from the gene precisely along establishedexon/intron splicing sites. Phylogenetic analysis of trnL-F sequence data revealed that they are closelyrelated species. This indicates that the intron was lost from the chloroplast genome before the divergence ofthe two Hedysarum species. It is concluded that this rare genomic structural mutation may have occurredonce during the evolution of land plants.