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

Abstract

AbstractLichen 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.