A cryptic intracellular green alga in Ginkgo biloba: ribosomal DNA markers reveal worldwide distribution

Abstract

Intracellular symbioses involving eukaryotic microalgae and a variety of heterotrophic protists and invertebrates are widespread, but are unknown in higher plants. Recently, we reported the isolation and molecular identification of a Coccomyxa-like green alga from in vitro cell cultures of Ginkgo biloba L. This alga resides intracellularly in an immature "precursor" form with a nonfunctional chloroplast, implying that algal photosynthetic activity has no role in this endosymbiosis. In necrotizing Ginkgo cells, precursors evolved into mature algae, proliferated, and were liberated into the culture medium after host cell bursting. In the present paper we demonstrate by molecular methods a worldwide distribution of the alga in planta. Endosymbiont-specific sequences of ribosomal DNA could be traced in Ginkgo tissues of each specimen examined from different geographic locations in Europe, North America, and Asia. The Ginkgo/Coccomyca association represents a new kind of intracellular, vertically inherited symbiosis. Storage bodies, probably of lipid nature, present in the cytoplasm of each partner suggest a possible involvement of the endosymbiont in metabolic pathways of its host.

Photobiont association and genetic diversity of the optionally lichenized fungus Schizoxylon albescens

“…The nucSSU and the ITS rDNA sequences show a high similarity to Coccomyxa lichen photobionts when performing BLAST searches in GenBank. The most similar sequences come from a unique algal endophyte of Ginkgo trees (Coccomyxa glaronensis, Tremouillaux-Guiller & Huss, 2007) and from a Coccomyxa parasitizing mussels (Rodríguez et al, 2008). Both the diagnostic morphological characteristics observed and the sequence data obtained thus indicate that these algae are closely related to Coccomyxa.…”

Molecular evidence for the evolution of ichnoviruses from ascoviruses by symbiogenesis

“…However, recent work has demonstrated that this evolutionary process was not restricted to bacteria. It also occurred between endocellular eukaryotes such as unicellular algae and fungal endophyte in plants [55,56]. Endosymbiogenesis was also proposed as the evolutionary mechanism that allowed some invertebrate viruses with a large double-stranded DNA genome related to the nudiviruses and the ascoviruses [22], to have led, respectively, to the origin of bracoviruses and ichnoviruses, which are currently recognized as forming two genera within the family Polydnaviridae.…”

Evaluating the Species Boundaries of Green Microalgae (Coccomyxa, Trebouxiophyceae, Chlorophyta) Using Integrative Taxonomy and DNA Barcoding with Further Implications for the Species Identification in Environmental Samples

“…Representatives of the genus Coccomyxa occur as free-living in terrestrial green biofilms, as soil algae and associated with mosses [22–25] as well as planktonic in limnic ecosystems [26–27]. Further, this genus participates in symbiotic associations with asco- and basidiomycetes [28–30], with higher plants [31] and is able to infest marine mussels [32, 33]. Coccomyxa even occurs as a contaminant in chemical solutions or distilled water in laboratories [34] or in the cooling water of a nuclear power plant [35].…”