Genomic analysis ofCoccomyxa viridis, a common low-abundance alga associated with lichen symbioses

Abstract

Lichen symbiosis is centered around a relationship between a fungus and a photosynthetic microbe, usually a green alga. In addition to their main photosynthetic partner (the photobiont), lichen symbioses can contain additional algae present in low abundance. The biology of these algae and the way they interact with the rest of lichen symbionts remains largely unknown. Here we present the first genome sequence of a non-photobiont lichen-associated alga.Coccomyxa viridiswas unexpectedly found in 12% of publicly available lichen metagenomes. With few exceptions, members of theCoccomyxa viridisclade occur in lichens as non-photobionts, potentially growing in thalli endophytically. The 45.7 Mbp genome ofC. viridiswas assembled into 18 near chromosome-level contigs, making it one of the most contiguous genomic assemblies for any lichen-associated algae. Comparing theC. viridisgenome to its close relatives revealed the presence of traits associated with the lichen lifestyle. The genome ofC. viridisprovides a new resource for exploring the evolution of the lichen symbiosis, and how symbiotic lifestyles shaped evolution in green algae.

High quality genome assembly and annotation (v1) of the eukaryotic terrestrial microalgaCoccomyxa viridisSAG 216-4

“…Several Coccomyxa species establish stable, mutualistic associations with fungi that result in the formation of complex three-dimensional architectures, known as lichens (Faluaburu et al, 2019;Gustavs et al, 2017;Jaag, 1933;Yahr et al, 2015;Zoller and Lutzoni, 2003). Others associate with vascular plants or lichens as endo-or epiphytes, respectively (Cao et al, 2018a;Cao et al, 2018b;Tagirdzhanova et al, 2023;Trémouillaux-Guiller et al, 2002), and frequently occur on the bark of trees (Kulichovà et al, 2014;Štifterovà and Neustupa, 2015) where they may interact with other microbes. One novel species was recently found in association with carnivorous plants, even though the nature of this relationship remains unclear (Sciuto et al, 2019).…”

“…Despite this ecological versatility, little is known about the molecular mechanisms that determine the various symbiotic lifestyles in Coccomyxa. One short read-based genome is available for C. subellipsoidea C-169 that was isolated on Antarctica where it occurred on dried algal peat (Blanc et al, 2012), whereas another high-quality genome has recently been made available for a non-symbiotic strain of C. viridis that was isolated from a lichen thallus (Tagirdzhanova et al, 2023). For Coccomyxa sp.…”