title: Transcriptional analysis of cell growth and morphogenesis in the unicellular green alga Micrasterias (Streptophyta), with emphasis on the role of expansin.
abstract: BACKGROUND
  Streptophyte green algae share several characteristics of cell growth and cell wall formation with their relatives, the embryophytic land plants. The multilobed cell wall of Micrasterias denticulata that rebuilds symmetrically after cell division and consists of pectin and cellulose, makes this unicellular streptophyte alga an interesting model system to study the molecular controls on cell shape and cell wall formation in green plants.
  
  
  RESULTS
  Genome-wide transcript expression profiling of synchronously growing cells identified 107 genes of which the expression correlated with the growth phase. Four transcripts showed high similarity to expansins that had not been examined previously in green algae. Phylogenetic analysis suggests that these genes are most closely related to the plant EXPANSIN A family, although their domain organization is very divergent. A GFP-tagged version of the expansin-resembling protein MdEXP2 localized to the cell wall and in Golgi-derived vesicles. Overexpression phenotypes ranged from lobe elongation to loss of growth polarity and planarity. These results indicate that MdEXP2 can alter the cell wall structure and, thus, might have a function related to that of land plant expansins during cell morphogenesis.
  
  
  CONCLUSIONS
  Our study demonstrates the potential of M. denticulata as a unicellular model system, in which cell growth mechanisms have been discovered similar to those in land plants. Additionally, evidence is provided that the evolutionary origins of many cell wall components and regulatory genes in embryophytes precede the colonization of land.
authors.affiliation: Laboratory of Protistology and Aquatic Ecology, Department of Biology, Ghent University, 9000 Gent, Belgium.
authors.forename: Katrijn
authors.initials: K
authors.lastname: Vannerum
authors.forename: Marie J J
authors.initials: MJ
authors.lastname: Huysman
authors.forename: Riet
authors.initials: R
authors.lastname: De Rycke
authors.forename: Marnik
authors.initials: M
authors.lastname: Vuylsteke
authors.forename: Frederik
authors.initials: F
authors.lastname: Leliaert
authors.forename: Jacob
authors.initials: J
authors.lastname: Pollier
authors.forename: Ursula
authors.initials: U
authors.lastname: Lütz-Meindl
authors.forename: Jeroen
authors.initials: J
authors.lastname: Gillard
authors.forename: Lieven
authors.initials: L
authors.lastname: De Veylder
authors.forename: Alain
authors.initials: A
authors.lastname: Goossens
authors.forename: Dirk
authors.initials: D
authors.lastname: Inzé
authors.forename: Wim
authors.initials: W
authors.lastname: Vyverman
mesh_terms: D000595:Amino Acid Sequence; D054458:Amplified Fragment Length Polymorphism Analysis; D002473:Cell Wall / Q000378:metabolism; D020869:Gene Expression Profiling; D058120:Micrasterias / Q000166:cytology* / Q000235:genetics* / Q000254:growth & development*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018749:RNA, Plant / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D010940:Plant Proteins; D018749:RNA, Plant; C095825:expansin protein, plant