title: Heveochlorella (Trebouxiophyceae): a little-known genus of unicellular green algae outside the Trebouxiales emerges unexpectedly as a major clade of lichen photobionts in foliicolous communities.
abstract: Foliicolous lichens are formed by diverse, highly specialized fungi that establish themselves and complete their life cycle within the brief duration of their leaf substratum. Over half of these lichen-forming fungi are members of either the Gomphillaceae or Pilocarpaceae, and associate with Trebouxia-like green algae whose identities have never been positively determined. We investigated the phylogenetic affinities of these photobionts to better understand their role in lichen establishment on an ephemeral surface. Thallus samples of Gomphillaceae and Pilocarpaceae were collected from foliicolous communities in southwest Florida and processed for sequencing of photobiont marker genes, algal cultivation and/or TEM. Additional specimens from these families and also from Aspidothelium (Thelenellaceae) were collected from a variety of substrates globally. Sequences from rbcL and nuSSU regions were obtained and subjected to Maximum Likelihood and Bayesian analyses. Analysis of 37 rbcL and 7 nuSSU algal sequences placed all photobionts studied within the provisional trebouxiophycean assemblage known as the Watanabea clade. All but three of the sequences showed affinities within Heveochlorella, a genus recently described from tree trunks in East Asia. The photobiont chloroplast showed multiple thylakoid stacks penetrating the pyrenoid centripetally as tubules lined with pyrenoglobuli, similar to the two described species of Heveochlorella. We conclude that Heveochlorella includes algae of potentially major importance as lichen photobionts, particularly within (but not limited to) foliicolous communities in tropical and subtropical regions worldwide. The ease with which they may be cultivated on minimal media suggests their potential to thrive free-living as well as in lichen symbiosis.
authors.affiliation: Department of Biological Sciences, Florida Gulf Coast University, Ft. Myers, Florida, 33965-6565, USA.
authors.forename: William B
authors.initials: WB
authors.lastname: Sanders
authors.affiliation: Departamento de Biogeoquímica y Ecología Microbiana, Museo Nacional de Ciencias Naturales (CSIC), C/Serrano 115-dpdo, E-28006, Madrid, Spain.
authors.forename: Sergio
authors.initials: S
authors.lastname: Pérez-Ortega
authors.affiliation: Committee on Evolutionary Biology, University of Chicago, 1025 E. 57th Street, Chicago, Illinois, 60637, USA.|Science & Education, The Field Museum, 1400 S. Lake Shore Drive, Chicago, Illinois, 60605, USA.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Nelsen
authors.affiliation: Botanical Garden and Botanical Museum Berlin, Königin-Luise-Straße 6-8, 14195, Berlin, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Lücking
authors.affiliation: Departamento de Biogeoquímica y Ecología Microbiana, Museo Nacional de Ciencias Naturales (CSIC), C/Serrano 115-dpdo, E-28006, Madrid, Spain.
authors.forename: Asunción
authors.initials: A
authors.lastname: de Los Ríos
mesh_terms: D020418:Algal Proteins / Q000235:genetics; D000460:Chlorophyta / Q000145:classification* / Q000235:genetics / Q000502:physiology*; D048028:DNA, Algal / Q000235:genetics; D005431:Florida; D008011:Lichens / Q000502:physiology*; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013559:Symbiosis
chemical_list: D020418:Algal Proteins; D048028:DNA, Algal
keywords: 
  Aspidothelium
  ; 
  Heveochlorella
  ; Gomphillaceae; Pilocarpaceae; Watanabea clade; foliicolous lichens; photobionts; phycobionts; pyrenoid; symbiont selection; “Chlorella”