Journal
FEMS MICROBIOLOGY ECOLOGY
Volume 83, Issue 2, Pages 310-323Publisher
OXFORD UNIV PRESS
DOI: 10.1111/j.1574-6941.2012.01474.x
Keywords
ITS; lichen symbiosis; phycobiont coexistence; Ramalina; rpb2; Trebouxia
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Funding
- Spanish Ministry of Science and Innovation [CGL2009-13429-C02-01/02]
- AECID [PCI_A_l024755/09]
- Generalitat Valenciana [PROMETEO 174/2008 GVA]
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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.
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