The genetic structure of the cosmopolitan three-partner lichenRamalina farinaceaevidences the concerted diversification of symbionts

Abstract

The epiphytic lichen Ramalina farinacea is distributed throughout the northern hemisphere in which the same two algal Trebouxia species (provisionally named TR1 and TR9) coexist in every thallus. Ramalina farinacea symbionts were characterized based on the two fungal nuclear loci (nrITS and rpb2) along with the primary and secondary structures of nrITS from each Trebouxia species in the Iberian Peninsula and Canary Islands. The results indicated a noticeable genetic differentiation between mycobionts from these two geographic areas and also suggested concerted changes in the three partners of a lichen symbiosis toward two clearly distinguishable 'holobiont' lineages. Modeling of ITS2 RNA secondary structures suggested their temperature sensitivity in TR1 but not in TR9, which was consistent with the observed superior physiological performance of TR9 phycobionts under relatively high temperatures. Both TR1 and TR9 phycobionts have been also found in a variety of taxonomically distinct lichens with a preferably Mediterranean distribution, being TR1 much more widespread than TR9. Our observations support a model in which ecological diversification and speciation of lichen symbionts in different habitats could include a transient phase consisting of associations with more than one photobiont in individual thalli. Such diversification is likely to be promoted by different physiological backgrounds.

Lichen Rehydration in Heavy Metal-Polluted Environments: Pb Modulates the Oxidative Response of Both Ramalina farinacea Thalli and Its Isolated Microalgae

“…1a). The sequence of six randomly selected bands was shown to be identical, or similar to previously published sequences for TR1 phycobionts [13,12]. To test the co-existence of TR9 in all thalli as previously demonstrated in [9], we used the 23Sps1 and cL781R primer pair (Fig.…”

“…The correct classification of the sample as R. farinacea was confirmed for six randomly selected thalli on the basis of the nrITS as described in [13] (accessions: KJ413040, KJ413041, KJ413042, KJ413043, KJ413044, KJ413045). BLAST searches against nucleotide sequences from the NCBI showed that the fungal partner effectively corresponded to R. farinacea.…”

“…In previous studies, we analysed the genetic structure of diverse populations of R. farinacea from the Iberian Peninsula, the Canary Islands and California [9,13]. Morphological and genetic evidence indicated that all the analysed thalli contained both Trebouxia TR1 and T. TR9 phycobionts at the same time.…”

“…A portion of the plastid 23SrDNA was PCR-amplified using the primers 23Sps1 5′-CAT GAC CAG GAT GAA GCT TG -3′, 23Sps2 5′-TAC TCA AGC CGA CAT TCT C -3′ and cL781R [9]. Amplification products were sequenced as previously described [13].…”

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).…”