An early-branching freshwater cyanobacterium at the origin of plastids ($)

originsofplasmidsPlastids are derived from an ancient endosymbiosis of a cyanobacterium, but which cyanobacteria are plastid’s nearest living relatives? Ponce-Toledo et al. generated an extensive phylogeny comprising numerous cyanobacteria and plastid-bearing eukaryotes (glaucophytes, red algae and green algae). Their data show that this nearest relative is the recently described freshwater cyanobacterium Gloeomargarita lithophora, which has a wide distribution in freshwater lakes but has never been found in a marine environment. This observation suggests that freshwater is the site of origin of the earliest photosynthetic eukaryotes. Curr. Biol. 10.1016/j.cub.2016.11.056