title: Chlamydia, cyanobiont, or host: who was on top in the ménage à trois?
abstract: The endosymbiont hypothesis proposes that photosynthate from the cyanobiont was exported to the cytosol of the eukaryote host and polymerized from ADP-glucose into glycogen. Chlamydia-like pathogens are the second major source of foreign genes in Archaeplastida, suggesting that these obligate intracellular pathogens had a significant role during the establishment of endosymbiosis, likely through facilitating the metabolic integration between the endosymbiont and the eukaryotic host. In this opinion article, we propose that a hexose phosphate transporter of chlamydial origin was the first transporter responsible for exporting photosynthate out of the cyanobiont. This connection pre-dates the recruitment of the host-derived carbon translocators on the plastid inner membranes of green and red algae, land plants, and photosynthetic organisms of higher order endosymbiotic origin.
authors.affiliation: Institute for Plant Biochemistry, Cluster of Excellence on Plant Sciences (CEPLAS), Heinrich-Heine-University, Universitätsstrasse 1, D-40225 Düsseldorf, Germany.
authors.forename: Fabio
authors.initials: F
authors.lastname: Facchinelli
authors.forename: Christophe
authors.initials: C
authors.lastname: Colleoni
authors.forename: Steven G
authors.initials: SG
authors.lastname: Ball
authors.forename: Andreas P M
authors.initials: AP
authors.lastname: Weber
mesh_terms: D002689:Chlamydia / Q000235:genetics* / Q000378:metabolism; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D058108:Glaucophyta / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D006003:Glycogen / Q000378:metabolism; D018087:Plastids / Q000235:genetics / Q000378:metabolism; D000461:Rhodophyta / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology; D013559:Symbiosis
chemical_list: D006003:Glycogen
keywords: endosymbiosis; metabolite transport; plastid evolution