Characterization of mycobionts of photomorph pairs in the Peltigerineae (lichenized ascomycetes) based on internal transcribed spacer sequences of the nuclear ribosomal DNA

The ''one fungus-two photomorphs'' hypothesis suggests that certain lichenized fungi can establish a symbiotic relationship with either a eukaryotic or a prokaryotic photobiont. Such pairs of photomorphs are well know from cephalodiate Peltigerineae. Using an ascomycete-specific primer we amplified the internal transcribed spacer region of the nrDNA repeat of the mycobiont from total ''lichen DNA'' extracts of Peltigera malacea, photomorphs of P. aphthosa, P. britannica, and P. leucophlebia, Nephroma expallidum, and photomorphs of N. arcticum. Comparisons of 5.8S sequences suggest that the sequences obtained belong to the mycobiont and thus, that the ascomycete-specific primer is adequate for amplifying fungal DNA from total lichen-DNA extracts. The strict identity of nucleotide sequences of the internal transcribed spacer region of the nrDNA repeat between joined-photomorphs supports the one fungus-two photomorphs hypothesis. Photomorphs may thus primarily reflect phenotypic plasticity of photomorphic fungi in response to changing environmental conditions. The cyanomorph recently reported for P. leucophlebia is shown to be based on a misidentified specimen of P. aphthosa. Comparisons of the ITS sequences further supports recognizing P. aphthosa, P. britannica, and P. leucophlebia at the species rather than the infraspecific level. (C) 1997 Academic Press.