How was photosynthesis established in eukaryotes? To gain insights into this fundamental step in the evolution of our planet, Debashish Bhattacharya at the Rutgers University and Jeffrey Boore at Genome Project Solutions, Inc. will determine to high coverage the 140 million base pair nuclear genome sequence of the unicellular alga Cyanophora paradoxa.
Cyanophora paradoxa is a member of the remaining group of photosynthetic eukaryotes (Glaucophyta) that still lacks a complete genome sequence. The single cyanobacterial primary endosymbiosis that gave rise to all plastids (e.g., chloroplasts) occurred in the common ancestor of Cyanophora, other algae, and plants. This was a pivotal and ancient (~1.5 billion years ago) event in the Earth's history that laid the foundation for modern terrestrial ecosystems.
A critical step in plastid establishment was the transfer of endosymbiont genes to the "host" nucleus. However, it is unclear whether this massive transfer was limited to genes strictly involved in plastid metabolism or whether the host profited from the captured genome to explore other novel functions via recruitment of genes from the cyanobacterium. The Cyanophora paradoxa genome sequence will enable us to rigorously test this idea in a relatively "simple" algal model.
Cyanophora paradoxa is also noteworthy because it is a free−living non−picoeukaryotic mesophile. The existing or nearly complete genomes from algal members of the Plantae are from non−flagellated thermoacidophilic red algae (Cyanidioschyzon merolae [16.5 Mbp], Galdieria sulphuraria [in progress, ca. 16 Mbp]) and from picoeukaryotic green algae (the prasinophytes Ostreococcus tauri [10.2 Mbp] and Micromonas pusilla spp. [ca. 15 Mbp]) that have highly reduced genomes. In the Cyanophora paradoxa genome, we expect to find the gene set (e.g., for flagellar use, photosynthesis, basic biochemistry) for a free−living autotroph that traces its origin to the Plantae ancestor. These aspects make Cyanophora paradoxa a highly attractive and a unique opportunity for a genome−sequencing program.