LAUSR

Primary plastids of the group Archaeplastida are descendants of a single cyanobacterial endosymbiont, while many other algal groups have obtained complex plastids, the so‐called secondary plastids, via several parallel endosymbiotic uptakes of primary plastid‐bearing algae. Integration of the endosymbiont into its host during primary and secondary endosymbiosis necessitated the establishment of transport mechanisms for metabolites, inorganic ions, and proteins across plastid envelope membranes. As a potential protein for exporting photosynthates out of primary plastids, homologs of bacterial UhpC‐type hexose‐phosphate transporters were found in algal members of the Archaeplastida. It has been proposed that plastidic UhpC‐type transporters have been acquired in the common ancestor of Archaeplastida by the lateral gene transfer from a bacterial lineage closely related to Chlamydiae. However, it remains unknown whether secondary plastid‐bearing organisms possess UhpC‐type transporters. In the present study, we investigated homologous genes of UhpC in diverse algae using available genome and transcriptome data. Our homology survey and phylogenetic analyses revealed that only dinoflagellates possess UhpC‐type transporters derived from an archaeplastidal lineage, whereas many other secondary plastid‐bearing organisms lack them. It is possible that UhpC‐type transporters are not essential in many secondary plastids because of the existence of other families of sugar phosphate transporters.