title: Losses, Expansions, and Novel Subunit Discovery of Adaptor Protein Complexes in Haptophyte Algae.
abstract: The phylum Haptophyta (Diaphoratickes) contains marine algae that perform biomineralization, extruding large, distinctive calcium carbonate scales (coccoliths) that completely cover the cell. Coccolith production is an important part of global carbon cycling; however, the membrane trafficking pathway by which they are secreted has not yet been elucidated. In most eukaryotes, post-Golgi membrane trafficking involves five heterotetrameric adaptor protein (AP) complexes, which impart cargo selection specificity. To better understand coccolith secretion, we performed comparative genomic, phylogenetic, and transcriptomic analyses of the AP complexes in Emiliania huxleyi strains 92A, Van556, EH2, and CCMP1516, and related haptophytes Gephyrocapsa oceanica and Isochrysis galbana; the latter has lost the ability to biomineralize. We show that haptophytes have a modified membrane trafficking system (MTS), as we found both AP subunit losses and duplications. Additionally, we identified a single conserved subunit of the AP-related TSET complex, whose expression suggests a functional role in membrane trafficking. Finally, we detected novel alpha adaptin ear and gamma adaptin ear proteins, the first of their kind to be described outside of opisthokonts. These novel ear proteins and the sculpting of the MTS may support the capacity for biomineralization in haptophytes, enhancing their ability to perform this highly specialized form of secretion.
authors.affiliation: Department of Cell Biology, 5-31 Medical Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2H7.
authors.forename: Laura J Y
authors.initials: LJ
authors.lastname: Lee
authors.affiliation: Department of Cell Biology, 5-31 Medical Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2H7.
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Klute
authors.affiliation: Department of Cell Biology, 5-31 Medical Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2H7. Electronic address: eherman@ualberta.ca.
authors.forename: Emily K
authors.initials: EK
authors.lastname: Herman
authors.affiliation: Department of Biological Sciences, California State University, San Marcos, California 92096, United States.
authors.forename: Betsy
authors.initials: B
authors.lastname: Read
authors.affiliation: Department of Cell Biology, 5-31 Medical Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2H7.
authors.forename: Joel B
authors.initials: JB
authors.lastname: Dacks
mesh_terms: D020418:Algal Proteins / Q000235:genetics* / Q000378:metabolism; D002113:Calcification, Physiologic; D016678:Genome; D006056:Golgi Apparatus / Q000502:physiology; D058087:Haptophyta / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D021381:Protein Transport; D017422:Sequence Analysis, DNA
chemical_list: D020418:Algal Proteins
keywords: Haptophyta; adaptin; adaptor protein; biomineralization; membrane trafficking; secretion.