The four genomes of the alga Pyrenomonas salina (Cryptophyta)

Abstract Cryptomonads are a group of unicellular eukaryotic algae with unusual features. First, their plastids are surrounded by four membranes and second, between the two pairs of membranes there is a plasmatic compartment. This supernumerary eukaryotic compartment of the cryptomonad cell is devoid of mitochondria but contains starch grains, 80S ribosomes and a small vestigial eukaryotic nucleus called the nucleomorph. Isolation and characterization of the four genomes (from mitochondrion, plastid, nucleus and nucleomorph) of one cryptomonad, Pyrenomonas salina , demonstrates that the cryptomonads have originated from an unicellular organism related to green algae which endosymbiotically took up a eukaryotic protist related to the red algae.