Figure 1
A diagram showing the course of the establishment of secondary chloroplasts, illustration of the cryptophyte Guillardia theta and distribution of chloroplast division proteins in eukaryotes. (a) Schematic view of organelle reduction and membrane heredity through secondary endosymbiosis. The green double membrane, sky-blue membrane and blue membrane represent the inner and the outer chloroplast envelope membranes, periplastidal membrane and chloroplast ER, respectively. The space indicated in yellow is the periplastidal compartment (PPC), which is homogeneous with the cytoplasm in primary endosymbiotic algae. The evolutionary stage of cryptophytes and chlorarachniophytes corresponds to secondary alga that possesses a nucleomorph. (b) Schematic drawing of the ultrastructure of G. theta based on McKerracher & Gibbs (1982). Chl, chloroplast; N, nucleus; Nm, nucleomorph; Py, pyrenoid; S, starch; Mt, mitochondria; G, Golgi body. The nucleomorph is located in the PPC between the outer chloroplast envelope (white arrowheads) and the periplastidal membrane (black arrowheads). (c) Distribution of chloroplast division proteins that are descended from the cyanobacterial ancestor of chloroplasts and the eukaryotic host (based on Miyagishima et al.10 and Hirakawa & Ishida 2015). The “Chl”, “N” and “Nm” in each column indicate that the gene is encoded in the chloroplast, nucleus and nucleomorph genome, respectively. The hyphen indicates that the gene is not found in the corresponding organism. Proteins encoded in the cyanobacterial or chloroplast genome are boxed in green, proteins encoded in the nuclear genome of primary algae or plants are boxed in pink and proteins encoded in the nuclear genome of secondary algae are boxed in blue. The accession numbers of the amino acid sequences are listed in Supplementary Table 1.
