Plastid Origin and Evolution: New Models Provide Insights into Old Problems

Algae are defined by their photosynthetic organelles (plastids) that have had multiple independent origins in different phyla. These instances of organelle transfer significantly complicate inference of the tree of life for eukaryotes because the intracellular gene transfer (endosymbiotic gene transfer [EGT]) associated with each round of endosymbiosis generates highly chimeric algal nuclear genomes. In this Update we review the current state in the field of endosymbiosis research with a focus on the use of the photosynthetic amoeba Paulinella to advance our knowledge of plastid evolution and current ideas about the origin of the plastid translocons. These research areas have been revolutionized by the advent of modern genomic approaches.