Morphological and phylogenetic study of algal partners associated with the lichen-forming fungus Tephromela atra from the Mediterranean region

Abstract

Recent DNA sequence analyses have revealed the diversity of algal partners in lichen symbioses. Although morphologically similar, different genetic lineages of photobionts are detected in wide geographic ranges of the same lichen fungal species. We studied the photobiont of the genus Trebouxia, which are known as partners of diverse lichen-forming fungal species in the Mediterranean region. We studied the phylogeny of these algae with a multilocus dataset including three loci: ITS, rbcL, and actin type I gene. The two lineages found, informally named Trebouxia sp. 1 and Trebouxia sp. 2, are related to Trebouxia arboricola/decolorans. The cultivation under axenic conditions succeeded only for one of them so far. We used light microscopy, confocal laser scanning microscopy and transmission electron microscopy for phenotypic characterisation. The ultrastructural characters currently used to describe species in the genus do not support the segregation of Trebouxia sp.1 from Trebouxia arboricola. The preferential presence in Mediterranean climates of these strains suggests eco-physiological adaptation. Despite their asexuality in long living lichen symbioses, coccoid algal lichen partners have apparently diversified genetically and physiologically.

Green-algal photobiont diversity (Trebouxia spp.) in representatives of Teloschistaceae (Lecanoromycetes, lichen-forming ascomycetes)

“…Accordingly, only a few experts worldwide were able to identify the photobionts of lichenforming fungi at species level. Since the advent of molecular techniques, the timeconsuming isolation and culturing has been largely avoided; instead, photobiont-specific molecular markers applied to whole lichen DNA has facilitated photobiont identification at the species level (Kroken & Taylor 2000;Dahlkild et al 2001;Helms et al 2001;Piercey-Normore & DePriest 2001;Tibell 2001;Romeike et al 2002;Tibell & Beck 2002;Helms 2003;Piercey-Normore 2004Yahr et al 2004Yahr et al , 2006Blaha et al 2006;Guzow-Krzeminska 2006;Muggia et al 2008Muggia et al , 2010Francisco De Oliveira et al 2012). Based on increasing numbers of entries in databases, the studies above have gained novel insights into photobiont diversity and phylogenies.…”

Substratum preference of two species of Xanthoparmelia

“…arboricola clade (Leavitt et al 2013). While the actin gene sequence is not known to be the best gene for species determination or barcoding in algae (Buchheim et al 2011;Saunders & Kucera 2010;Saunders & McDevit 2012), it provides an indication of similarity in identity and has been used to infer phylogenetic relationships in other studies (Fern andez-Mendoza et al 2011;Muggia et al 2010;Piercey-Normore 2006, 2009Kroken and Taylor 2000).…”

Coordinated ultrastructural and phylogenomic analyses shed light on the hidden phycobiont diversity of Trebouxia microalgae in Ramalina fraxinea

“…Under the assumption of high flexibility in the specificity and ecological selection of the phycobionts, the ability to establish new fungus-phycobiont associations has enabled lichens to colonize varied and wide-ranging habitats (Doering and Piercey-Normore, 2009). Several studies have demonstrated that lichen mycobionts associate with different phycobionts under different environmental conditions, or in different geographical regions (Blaha et al, 2006;Casano et al, 2011;Cordeiro et al, 2005;del Campo et al, 2013;Muggia et al, 2008Muggia et al, , 2010Peksa and Škaloud, 2011;Schmull et al, 2011;Fedrowitz et al, 2012;Rikkinen, 2013).…”