Chimeric origins of ochrophytes and haptophytes revealed through an ancient plastid proteome

• Published in: eLife Vol. 6
• Main Authors: Dorrell, Richard G, Gile, Gillian, McCallum, Giselle, Méheust, Raphaël, Bapteste, Eric P, Klinger, Christen M, Brillet-Guéguen, Loraine, Freeman, Katalina D, Richter, Daniel J, Bowler, Chris
• Format: Journal Article
• Language: English
• Published: England eLife Science Publications, Ltd 12.05.2017; eLife Sciences Publications Ltd; eLife Sciences Publication; eLife Sciences Publications, Ltd
• Subjects: Algae; Bacillariophyta; Cell Biology; Chlorophyta; Chloroplast Proteins - genetics; chromalveolate; Cytoplasm; diatom; Evolution; Evolution, Molecular; Genomes; Genomics and Evolutionary Biology; Haptophyta - classification; Haptophyta - genetics; HPPG; Life Sciences; Methods; Microorganisms; Nuclei; Phylogeny; Physiological aspects; plastid protein import; Plastids; Proteins; Proteomes; Proteomics; Rhodophyta; shopping bag model; Stramenopiles - classification; Stramenopiles - genetics; plastid protein import; cell biology; evolutionary biology; shopping bag model; algae; genomics; none; diatom; HPPG; chromalveolate
• ISSN: 2050-084X; 2050-084X
• DOI: 10.7554/elife.23717

Plastids are supported by a wide range of proteins encoded within the nucleus and imported from the cytoplasm. These plastid-targeted proteins may originate from the endosymbiont, the host, or other sources entirely. Here, we identify and characterise 770 plastid-targeted proteins that are conserved across the ochrophytes, a major group of algae including diatoms, pelagophytes and kelps, that possess plastids derived from red algae. We show that the ancestral ochrophyte plastid proteome was an evolutionary chimera, with 25% of its phylogenetically tractable nucleus-encoded proteins deriving from green algae. We additionally show that functional mixing of host and plastid proteomes, such as through dual-targeting, is an ancestral feature of plastid evolution. Finally, we detect a clear phylogenetic signal from one ochrophyte subgroup, the lineage containing pelagophytes and dictyochophytes, in plastid-targeted proteins from another major algal lineage, the haptophytes. This may represent a possible serial endosymbiosis event deep in eukaryotic evolutionary history.