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Chromalveolate
Clockwise from top-left: a haptophyte, some diatoms, a water mold, a cryptomonad, and Macrocystis, a phaeophyte
Scientific classification
Domain: Eukarya
(unranked) Bikonta
(unranked): Corticata
Kingdom: Chromalveolata*
Phyla

Chromalveolata is a eukaryote supergroup first proposed by Thomas Cavalier-Smith as a refinement of his kingdom Chromista, which was first proposed in 1981. It was proposed to represent the result of a single secondary endosymbiosis of a line descending from a bikont with a red alga[1] that became the progenitor of chlorophyll c containing plastids.

Contents

Groups and classification

As of 2006, it was often regarded as one of six major clades of eukaryotes,[2] although it is hotly debated and does not appear to be monophyletic as originally proposed.[2][3]

Though several groups, such as the ciliates and the water molds, have lost the ability to photosynthesize, most are autotrophic. All photosynthetic chromalveolates use chlorophylls a and c, and many use accessory pigments.

Chromalveolates share similar Glyceraldehyde 3-phosphate dehydrogenase proteins.[4]

Chromalveolates are not given any formal taxonomical classification, but may be considered a “kingdom”.

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SA/SAR

Specifically, recent expressed sequence tag analysis has suggested Rhizaria groups in a clade dubbed the SAR supergroup with Alveolata and stramenopiles.[5][6]

Though "SAR" includes three major groups ("S" for "Stramenopiles" or Heterokontophyta, "A" for Alveolata, and "R" for Rhizaria), most phylogenies show the "S" and "A" to be more closely related to each other than the "R", thus preserving a reduced chromalveolate clade (after removing Hacrobia).

Hacrobia

Other groups are not considered part of the SAR clade. These include Haptophyta and Cryptophyta.

Evolutionary relationship

Chromalveolata is part of the bikonts, which also comprise the Archaeplastida, the Rhizaria, the Excavata, and some smaller, unresolved groups such as the Apusozoa and the Centrohelida. As bikonts, they all descend from a heterotrophic eukaryote with two flagella. It is also thought that the Chromalveolata share a closer relationship with the Archaeplastida than with the other groups, and some have proposed a clade called Corticata for this grouping.

Historically, many chromalveolates were considered plants, with their cell walls, photosynthetic ability, and in some cases their morphological resemblance to the Embryophyta. However, when the five-kingdom system took prevalence over the animal-plant dichotomy, most chromalveolates were put into the kingdom Protista, with the water molds and slime nets put into the kingdom Fungi, and the brown algae staying in the plant kingdom. Later, Chromalveolata was proposed as a monophyletic group, but the monophyly of this group is not yet established.[7][2]

Other groups which may be included within, or related to, Chromalveolates, are:

Morphology

Chromalveolates, unlike other groups with multicellular representatives, do not have very many common morphological characteristics. Each major subgroup has certain unique features, including the alveoli of the Alveolata, the haptonema of the Haptophyta, the ejectisome of the Crytophyta, and the two different flagella of the Heterokontophyta. However, none of these features are present in all of the groups.

The only common chromalveolate features are these:

  • The shared origin of chloroplasts, as mentioned above
  • Presence of cellulose in most cell walls

Since this is such a diverse group, it is difficult to summarize shared chromalveolate characteristics.

Ecological role

A potato plant infected with Phytophthora infestans.

Many chromalveolates affect our ecosystem in enormous ways. Some of these organisms can be very harmful. Dinoflagellates produce red tides which can devastate fish populations and intoxicate oyster harvests. Apicomplexans are some of the most successful specific parasites to animals. Water molds cause several plant diseases. In fact, it was a water mold, Phytophthora infestans, that caused the Irish potato famine.

A Californian kelp forest.

However, many chromalveolates are vital members of our ecosystem. Diatoms are one of the major photosynthetic producers, and as such produce much of the oxygen we breathe, and also take in much of the carbon dioxide from the atmosphere. Brown algae, most specifically kelps, create underwater "forest" habitats for many marine creatures, and provide a large portion of the diet of coastal communities.

Chromalveolates also provide many products that we use. The algin in brown algae is used a food thickener, most famously in ice cream. The siliceous shells of diatoms have many uses, such as in reflective paint, in toothpaste, or as a filter, in what is known as diatomaceous earth.

References

  1. ^ Keeling PJ (2009). "Chromalveolates and the evolution of plastids by secondary endosymbiosis". J. Eukaryot. Microbiol. 56 (1): 1–8. doi:10.1111/j.1550-7408.2008.00371.x. PMID 19335769. http://dx.doi.org/10.1111/j.1550-7408.2008.00371.x.  
  2. ^ a b c Laura Wegener Parfrey, Erika Barbero, Elyse Lasser, Micah Dunthorn, Debashish Bhattacharya, David J Patterson, and Laura A Katz (2006 December). "Evaluating Support for the Current Classification of Eukaryotic Diversity". PLoS Genet. 2 (12): e220. doi:10.1371/journal.pgen.0020220. PMID 17194223. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1713255.  
  3. ^ Harper, J. T., Waanders, E. & Keeling, P. J. 2005. On the monophyly of chromalveolates using a six-protein phylogeny of eukaryotes. Int. J. System. Evol. Microbiol., 55, 487-496. [1]
  4. ^ Takishita K, Yamaguchi H, Maruyama T, Inagaki Y (2009). "A hypothesis for the evolution of nuclear-encoded, plastid-targeted glyceraldehyde-3-phosphate dehydrogenase genes in "chromalveolate" members". PLoS ONE 4 (3): e4737. doi:10.1371/journal.pone.0004737. PMID 19270733. PMC 2649427. http://dx.plos.org/10.1371/journal.pone.0004737.  
  5. ^ Fabien Burki, Kamran Shalchian-Tabrizi, Marianne Minge, Åsmund Skjæveland, Sergey I. Nikolaev, Kjetill S. Jakobsen, Jan Pawlowski (2007). "Phylogenomics Reshuffles the Eukaryotic Supergroups". PLoS ONE 2 (8): e790. doi:10.1371/journal.pone.0000790. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0000790.  
  6. ^ Kim, E; Graham, Le (Jul 2008). "EEF2 analysis challenges the monophyly of Archaeplastida and Chromalveolata." (Free full text). PLoS ONE 3 (7): e2621. doi:10.1371/journal.pone.0002621. PMID 18612431. PMC 2440802. http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002621.  
  7. ^ Burki F, Shalchian-Tabrizi K, Minge M, Skjæveland Å, Nikolaev SI, et al. (2007). "Phylogenomics Reshuffles the Eukaryotic Supergroups". PLoS ONE 2 (8: e790): e790. doi:10.1371/journal.pone.0000790.  
  8. ^ Shalchian-Tabrizi K, Eikrem W, Klaveness D, Vaulot D, Minge M, Le Gall F, Romari K, Throndsen J, Botnen A, Massana R, Thomsen H, Jakobsen K (2006). "Telonemia, a new protist phylum with affinity to chromist lineages". Proc Biol Sci 273 (1595): 1833–42. doi:10.1098/rspb.2006.3515. PMID 16790418.  

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