title: Gene functionalities and genome structure in Bathycoccus prasinos reflect cellular specializations at the base of the green lineage.
abstract: BACKGROUND
  Bathycoccus prasinos is an extremely small cosmopolitan marine green alga whose cells are covered with intricate spider's web patterned scales that develop within the Golgi cisternae before their transport to the cell surface. The objective of this work is to sequence and analyze its genome, and to present a comparative analysis with other known genomes of the green lineage.
  
  
  METHODS
  Its small genome of 15 Mb consists of 19 chromosomes and lacks transposons. Although 70% of all B. prasinos genes share similarities with other Viridiplantae genes, up to 428 genes were probably acquired by horizontal gene transfer, mainly from other eukaryotes. Two chromosomes, one big and one small, are atypical, an unusual synapomorphic feature within the Mamiellales. Genes on these atypical outlier chromosomes show lower GC content and a significant fraction of putative horizontal gene transfer genes. Whereas the small outlier chromosome lacks colinearity with other Mamiellales and contains many unknown genes without homologs in other species, the big outlier shows a higher intron content, increased expression levels and a unique clustering pattern of housekeeping functionalities. Four gene families are highly expanded in B. prasinos, including sialyltransferases, sialidases, ankyrin repeats and zinc ion-binding genes, and we hypothesize that these genes are associated with the process of scale biogenesis.
  
  
  CONCLUSIONS
  The minimal genomes of the Mamiellophyceae provide a baseline for evolutionary and functional analyses of metabolic processes in green plants.
authors.forename: Hervé
authors.initials: H
authors.lastname: Moreau
authors.forename: Bram
authors.initials: B
authors.lastname: Verhelst
authors.forename: Arnaud
authors.initials: A
authors.lastname: Couloux
authors.forename: Evelyne
authors.initials: E
authors.lastname: Derelle
authors.forename: Stephane
authors.initials: S
authors.lastname: Rombauts
authors.forename: Nigel
authors.initials: N
authors.lastname: Grimsley
authors.forename: Michiel
authors.initials: M
authors.lastname: Van Bel
authors.forename: Julie
authors.initials: J
authors.lastname: Poulain
authors.forename: Michaël
authors.initials: M
authors.lastname: Katinka
authors.forename: Martin F
authors.initials: MF
authors.lastname: Hohmann-Marriott
authors.forename: Gwenael
authors.initials: G
authors.lastname: Piganeau
authors.forename: Pierre
authors.initials: P
authors.lastname: Rouzé
authors.forename: Corinne
authors.initials: C
authors.lastname: Da Silva
authors.forename: Patrick
authors.initials: P
authors.lastname: Wincker
authors.forename: Yves
authors.initials: Y
authors.lastname: Van de Peer
authors.forename: Klaas
authors.initials: K
authors.lastname: Vandepoele
mesh_terms: D001482:Base Composition; D000460:Chlorophyta / Q000145:classification / Q000235:genetics*; D032461:Chromosomes, Plant / Q000235:genetics*; D019143:Evolution, Molecular; D023061:Gene Order; D022761:Gene Transfer, Horizontal; D018745:Genome, Plant / Q000235:genetics*; D023281:Genomics; D007438:Introns; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D010802:Phylogeny; D017422:Sequence Analysis, DNA
chemical_list: D019158:N-Acetylneuraminic Acid