Vesicles bearing Toxoplasma apicoplast membrane proteins persist following loss of the relict plastid or Golgi body disruption

• Published in: PloS one 2014-11, Vol.9 (11), p.e112096
• Main Authors: Bouchut, Anne, Geiger, Jennifer A, DeRocher, Amy E, Parsons, Marilyn
• Format: Article
• Language: English
• Subjects: Acquired immune deficiency syndrome; AIDS; Antigens; Apicomplexa; Apicoplasts - metabolism; Arabidopsis; Bearing; Biology and Life Sciences; Biomedical research; Biosynthesis; Brefeldin A; Chloroplasts; Direct flow; Endoplasmic reticulum; Fatty acids; Gene Expression Regulation; Genomes; Golgi apparatus; Golgi Apparatus - metabolism; Guanosine triphosphatases; Guanosinetriphosphatase; HIV; Human immunodeficiency virus; Immunofluorescence; Lipids; Malaria; Medicine and Health Sciences; Membrane proteins; Membrane trafficking; Membrane vesicles; Membranes; Microscopy; Nuclei; Parasites; Peptides; Promoter Regions, Genetic; Protein Biosynthesis; Protein Transport; Proteins; Proteomes; Protozoan Proteins - metabolism; Rodents; Toxoplasma - metabolism; Toxoplasma gondii; Transport Vesicles - metabolism; Vector-borne diseases; Vesicles
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0112096

Toxoplasma gondii and malaria parasites contain a unique and essential relict plastid called the apicoplast. Most apicoplast proteins are encoded in the nucleus and are transported to the organelle via the endoplasmic reticulum (ER). Three trafficking routes have been proposed for apicoplast membrane proteins: (i) vesicular trafficking from the ER to the Golgi and then to the apicoplast, (ii) contiguity between the ER membrane and the apicoplast allowing direct flow of proteins, and (iii) vesicular transport directly from the ER to the apicoplast. Previously, we identified a set of membrane proteins of the T. gondii apicoplast which were also detected in large vesicles near the organelle. Data presented here show that the large vesicles bearing apicoplast membrane proteins are not the major carriers of luminal proteins. The vesicles continue to appear in parasites which have lost their plastid due to mis-segregation, indicating that the vesicles are not derived from the apicoplast. To test for a role of the Golgi body in vesicle formation, parasites were treated with brefeldin A or transiently transfected with a dominant-negative mutant of Sar1, a GTPase required for ER to Golgi trafficking. The immunofluorescence patterns showed little change. These findings were confirmed using stable transfectants, which expressed the toxic dominant-negative sar1 following Cre-loxP mediated promoter juxtaposition. Our data support the hypothesis that the large vesicles do not mediate the trafficking of luminal proteins to the apicoplast. The results further show that the large vesicles bearing apicoplast membrane proteins continue to be observed in the absence of Golgi and plastid function. These data raise the possibility that the apicoplast proteome is generated by two novel ER to plastid trafficking pathways, plus the small set of proteins encoded by the apicoplast genome.