An exceptional group-I intron-like insertion in the SSU rDNA of lichen mycobionts

An exceptional group-I intron-like insertion at position 940 of the nuclear small subunit rDNA is found in lichen mycobionts of the families Parmeliac eae and Lecanoraceae. This shared insertion site is exceptional as it follo ws a G. Although several features of the self-splicing Tetrahymena intron a re missing, the conserved structure of the presumed core region indicates t hat the new intron-like insertion which is missing in mature transcripts, i n not part a silenced ribosomal repeat. It is unlikely that the new inserti on is horizontally transferred from the adjacent position 943. A phylogenet ic analysis indicates congruence with lichen phylogeny and suggests that th e insertion has been vertically inherited.