Characterization of Mycobionts of Photomorph Pairs in the Peltigerineae (Lichenized Ascomycetes) Based on Internal Transcribed Spacer Sequences of the Nuclear Ribosomal DNA

Abstract

Goffinet, B., and Bayer, R. J. 1997. Characterization of mycobionts of photomorph pairs in the Peltigerineae (lichenized ascomycetes) based on internal transcribed spacer sequences of the nuclear ribosomal DNA. Fungal Genetics and Biology 21, 228-237. The 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 ascomycetespecific 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. r 1997 Academic Press

Phylogenetic Revision of the GenusPeltigera(Lichen‐Forming Ascomycota) Based on Morphological, Chemical, and Large Subunit Nuclear Ribosomal DNA Data

“…Holtan-Hartwig (1993) noted that the capability of some Peltigera mycobionts to develop bi-and trimembered thalli is the main reason why a dichotomous classification of this genus based solely on photobiont composition is artificial. Results based on ITS sequences from Peltigera (Goffinet and Bayer 1997), as well as on RFLP analysis of the LSU nrDNA and Southern hybridization from Sticta and Pseudocyphellaria (Armaleo and Clerc 1991), support the hypothesis that the same fungus can form a bi-and trimembered symbiotic association. However, more sensitive methods or more variable portions of the fungal genome could reveal, for a given species, that the fungus interacting with the green alga is different from the one associated with the cyanobacterium.…”

“…The latter two species are often difficult to distinguish morphologically and sometimes also chemically. Goffinet and Bayer (1997) already pointed out the relatively high genetic divergence between P. leucophlebia and P. aphthosa compared to P. britannica and P. aphthosa. One feature that demarcates section Peltidea (P. leucophlebia and P. nigripunctata) is their inability to produce cyanomorphs.…”

“…This hypothesis was based on the observation that a remarkable number of lichenicolous fungi occur exclusively on Peltigera and also on the ascomatal ontogeny, ascus structure, and wide geographical distribution of many Peltigera species. Other molecular studies were designed to determine if the same mycobiont was responsible for both photomorphs within the P. aphthosa group and to study phylogenetic relationships among photomorphs (Goffinet and Bayer 1997). Only recently was the genetic variation of those cyanobacteria associated with Peltigera investigated at the population level and its possible implications for the system- Corbett and Young 1966a;Huneck et al 197312 Dolichorrhizin 15a-acetoxyhopan-22-ol Zopf 1909Corbett and Young 1966b;Kurokawa et al 1966;Takahashi et al 197015 Zeorin Hopane-6a,22-diol Zopf 1909Kurokawa et al 1966 16 Phlebic acid A 28-acetoxy-22-hydroxyhopan-23-carboxylic acid Kurokawa et al 1966;Takahashi et al 1969 17 Phlebic acid B 22-hydroxyhopan-23-carboxylic acid Kurokawa et al 1966;Takahashi et al 197020 ?…”

Tansley Review No. 116

“…Within a thallus, among cephalodia of a thallus, or between bipartite and tripartite morphotypes of a thallus, only one Nostoc strain is reported (Armaleo & Clerc, 1991 ;Goward et al, 1995 ;Goffinet & Bayer, 1997 ;Miao et al, 1997 ;. Lack of diversity within a thallus is consistent with a single event of cyanobiont acquisition during the formation of a bipartite thallus and the formation of new cephalodia by cyanobiont acquisition from older ones.…”

Spatial patterns of photobiont diversity in some Nostoc‐containing lichens

“…Cephalodia can occur either on thallus surfaces (external cephalodia) or in the medulla (internal cephalodia) (Nash, 1996). The mycobionts of cephalodiate lichens can sometimes produce different morphotypes in association with green algal or cyanobacterial photobionts (Armaleo & Clerc, 1991 ;Goffinet & Bayer, 1997). Free-living morphotypes, which contain only cyanobacteria or only green algae are called cyanosymbiodemes or chlorosymbiodemes, respectively (Renner & Galloway, 1982).…”