The hidden diversity of lichenised Trebouxiophyceae (Chlorophyta)

Abstract:

The class Trebouxiophyceae is comprised of coccoid to ellipsoid unicells, filaments, blades and colony-forming species of green algae occurring in diverse terrestrial and aquatic environments. Some representatives have evolved parasitic heterotrophic lifestyles, others have been investigated for their biotechnological potential and others have evolved as integral components of lichen symbioses. In this review, we provide an overview of the current understanding of diversity, taxonomy and evolutionary context for the important lichen-forming algal class Trebouxiophyceae (Chlorophyta). In particular, we focus on members of the family Trebouxiaceae (Trebouxiales), the best-known, most widespread and most species-rich group of terrestrial, lichenised green algae. Recent investigations on the diversity of lichen phycobionts demonstrate the importance of implementing integrative taxonomic approaches. Therefore, combining analyses of morphological and anatomical traits with genetic data has improved our perspective of diversity in lichenised algae. More accurate recognition of diversity in Trebouxiophyceae will enhance our understanding of phylogenetic relationships and trait evolution, specimen identification in genomic and meta–bar-coding studies and patterns of specificity and selectivity among the lichen symbionts. We conclude with a discussion of the roles and transformative potential of high-throughput sequencing in research related to lichen-associated algae.

Key Words::

• Asterochloris
• Coexistence
• Ecology
• Genomic
• Microalgae
• Phylogenetics
• Species
• Systematics

ACKNOWLEDGEMENTS

L.M. was supported by the Austrian Science Foundation for financial support (FWF Herta-Firnberg Project T481-B20), and E.B.'s research is supported by the projects Ministerio de Economia y Competitividad and FEDER (MINECO, Spain; CGL2016-391 79158-P) and Excellence in Research (Generalitat Valenciana, Spain; PROMETEO/2017/039). We are thankful to Theodora Kopun for help in the lab and to Matthew P. Nelsen and Martin Grube for their constructive discussions. We also thank all the participants in the Trebouxia Workshop held in Trieste 2016: Andreas Beck, Franceso dal Grande, Garima Singh, Patricia Moya, Arantxa Molins, Pedro Carrasco, Myriam Catalá, Fernando Fernández-Mendoza, Sergio Pérez Ortega, Martin Kukwa, Beata Guzow-Krzemińska, Heath O'Brien, Pavel Škaloud, Ondrej Peksa, Tereza Ridka, Andres Sadowsky, Elfie Stocker-Wörgötter, Ulrike Ruprecht, Anna Favre, Claudio G. Ametrano, Elisa Banchi, Alice Montagner, Fabio Candotto-Carniel and Mauro Tretiach.