Prasinophyceae

Prasinophyceae
Scientific classification
Domain: Eukaryota
Kingdom: Viridiplantae
Division: Chlorophyta
Class: Prasinophyceae
T.Christensen ex P.C.Silva 1980
Orders[1]

The Prasinophytes are a class of unicellular green algae in the Division Chlorophyta.[2] Prasinophytes mainly include marine planktonic species, as well as some freshwater representatives.[2][3] The prasinophytes are morphologically diverse, including flagellates with one to eight flagella and non-motile (coccoid) unicells. The cells of many species are covered with organic body scales; others are naked.[3] One well known genus is Ostreococcus, considered to be the smallest (ca. 0.95 μm) free-living eukaryote,[4] found in marine waters world wide. Prasinophytes have simple cellular structures, containing a single chloroplast and a single mitochondrion. The genomes are relatively small compared to other eukaryotes (about 12 Mbp for Ostreococcus[5][6] and 21 Mbp for Micromonas[7]).

Recent studies agree that the prasinophytes are a non-evolutionary grouping (paraphyletic) of chlorophyte green algae from different clades. Alternative classifications of the chlorophytes have been proposed in which this class is replaced by at least six separate taxa.[8]

Ecology

Micromonas pusilla

A study of photosynthetic gene-sequence diversity (rbcL) in the Gulf of Mexico indicated that Prasinophytes are particularly prevalent at the Subsurface Chlorophyll Maximum (SCM)[9] and several different ecotypes of Ostreococcus have been detected in the environment.[10] These ecotypes were thought to be distinguished in the environment by their adaptation to light intensities. O. lucimarinus was isolated from a high-light environment[11] and observed year-round in the coastal North Pacific Ocean.[12] RCC141 was considered low-light, because it was isolated from the lower euphotic zone. These strains, or ecotypes, were later shown to live in different habitats (open-ocean or mesotrophic) and their distributions do not appear to be connected to light availability.[13] O. tauri was isolated from a coastal lagoon and appears to be light-polyvalent. Genetic data indicates that distinct molecular differences exist between the different ecotypes that have been detected.[14]

Phylogeny

Recent studies agree that the prasinophytes are not a natural group, being highly paraphyletic.[8][15][3][16] Relationships among the groups making up the Chlorophyta are not fully resolved. The cladogram produced by Leliaert et al. 2011[3] is shown below. The blue shaded groups are or have traditionally been placed in the Prasionophyceae[2]). The species Mesostigma viride has been shown to be a member of the Streptophyta rather than the Chlorophyta.
Chlorophyta







Ulvophyceae

Chlorophyceae

Trebouxiophyceae

Chlorodendrophyceae

Pedinophyceae

"CCMP1205 clade"

Picocystis clade ("prasinophyte clade VII")

Pyramimonadales ("prasinophyte clade I")

Mamiellales ("prasinophyte clade II")

Dolichomastigales

Monomastigales

Pycnococcaceae ("prasinophyte clade V")

Nephroselmidophyceae ("prasinophyte clade III")

Prasinococcales ("prasinophyte clade VI")

Palmophyllales



Streptophyta

Chlorokybophyceae

Mesostigmatophyceae

Klebsormidiophyceae

Charophyceae

Zygnematophyceae

Coleochaetophyceae

Land plants







References

  1. ↑ Guiry, M.D. & Guiry, G.M. (2007). "Class: Prasinophyceae taxonomy browser". AlgaeBase version 4.2 World-wide electronic publication, National University of Ireland, Galway. Retrieved 2007-09-23.
  2. ↑ 2.0 2.1 2.2 Sym, S. D. and Pienaar, R. N. 1993. The class Prasinophyceae. In Round, F. E. and Chapman, D. J. (Eds) Progress in Phycological Research, Vol. 9. Biopress Ltd., Bristol, pp. 281-376.
  3. ↑ 3.0 3.1 3.2 3.3 Leliaert, Frederik; Verbruggen, Heroen; Zechman, Frederick W. (2011). "Into the deep: New discoveries at the base of the green plant phylogeny". BioEssays 33 (9): 683–692. doi:10.1002/bies.201100035. ISSN 0265-9247. PMID 21744372.
  4. ↑ Courties C, Vaquer A, Troussellier M, Lautier J, Chrétiennot-Dinet MJ, Neveux J, Machado C, Claustre H (1994). "Smallest eukaryotic organism". Nature 370 (6487): 255. doi:10.1038/370255a0.
  5. ↑ Derelle E et al. (2006). "Genome analysis of the smallest free-living eukaryote Ostreococcus tauri unveils many unique features". PNAS 103 (31): 11647–52. doi:10.1073/pnas.0604795103. PMC 1544224. PMID 16868079.
  6. ↑ Palenik, Brian et al. (2007). "The tiny eukaryote Ostreococcus provides genomic insights into the paradox of plankton speciation". PNAS 104 (18): 7705–7710. doi:10.1073/pnas.0611046104.
  7. ↑ Worden AZ et al. (2009). "Green evolution and dynamic adaptations revealed by genomes of the marine picoeukaryotes Micromonas". Science 324 (5924): 268–272. doi:10.1126/science.1167222. PMID 19359590.
  8. ↑ 8.0 8.1 Lewis, Louise A. & McCourt, R.M. (2004). "Green algae and the origin of land plants". Am. J. Bot. 91 (10): 1535–1556. doi:10.3732/ajb.91.10.1535. PMID 21652308.
  9. ↑ Wawrik B, Paul JH, Campbell L, Griffin D, Houchin L, Fuentes-Ortega A, Müller-Karger F (2003). "Vertical Structure of the Phytoplankton Community Associated with a Coastal Plume in the Gulf of Mexico". Marine Ecology Progress Series 251: 87–101. doi:10.3354/meps251087.
  10. ↑ Guillou L, Eikrem W, Chrétiennot-Dinnet MJ, Le Gall F, Massana R, Romari K, Pedros-Alio C, Vaulot D (2004). "Diversity of picoplanktonic Prasinophyceae assessed by direct SSU rDNA sequencing of environmental samples and novel isolates retrieved from oceanic and coastal marine ecosystems". Protist 155 (2): 193–214. doi:10.1078/143446104774199592. PMID 15305796.
  11. ↑ Worden AZ, Nolan JK, Palenik B (2004). "Assessing the dynamics and ecology of marine picophytoplankton: The importance of the eukaryotic component". Limnology and Oceanography 49 (1): 168–179. doi:10.4319/lo.2004.49.1.0168.
  12. ↑ Worden AZ (2006). "Picoeukaryote diversity in coastal waters of the Pacific Ocean". Aquatic Microbial Ecology 43 (2): 165–175. doi:10.3354/ame043165.
  13. ↑ Demir-Hilton E, Sudek S, Cuvelier ML, Gentemann CL, Zehr JP, Worden AZ (2011). "Global distribution patterns of distinct clades of the photosynthetic picoeukaryote Ostreococcus". ISME Journal 5 (7): 1095–1107. doi:10.1038/ismej.2010.209. PMC 3146286. PMID 21289652.
  14. ↑ Rodríguez F, Derelle E, Guillou L, Le Gall F, Vaulot D, Moreau H (2005). "Ecotype diversity in the marine picoeukaryote Ostreococcus (Chlorophyta, Prasinophyceae)". Environmental Microbiology 7 (6): 853–859. doi:10.1111/j.1462-2920.2005.00758.x. PMID 15892704.
  15. ↑ Becker, B. & Marin, B. (2009). "Streptophyte algae and the origin of embryophytes". Annals of Botany 103 (7): 999–1004. doi:10.1093/aob/mcp044. PMC 2707909. PMID 19273476.
  16. ↑ Marin, Birger (2012). "Nested in the Chlorellales or Independent Class? Phylogeny and Classification of the Pedinophyceae (Viridiplantae) Revealed by Molecular Phylogenetic Analyses of Complete Nuclear and Plastid-encoded rRNA Operons". Protist 163: 778–805. doi:10.1016/j.protis.2011.11.004.

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