Glaucophyte

Glaucophyta
Glaucocystis sp.
Scientific classification
Clade:	Archaeplastida
Division:	Glaucophyta Skuja 1948
Class
Glaucocystophyceae Schaffner 1922
Synonyms
Glaucocystophyta Kies & Kremer, 1986

The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments,^[1][2] less common today than they were during the Proterozoic.^[3] The stated number of species in the group varies from about 14 to 26.^[4][5][6] Together with the red algae (Rhodophyta) and the green algae plus land plants (Viridiplantae or Chloroplastida), they form the Archaeplastida.

The glaucophytes are of interest to biologists studying the evolution of chloroplasts as they may be similar to the original algal type that led to the red algae and green plants, i.e. glaucophytes may be basal Archaeplastida.^[1][7][4]

Unlike red and green algae, glaucophytes only have asexual reproduction.^[8]

Characteristics

The plastids of glaucophytes are known as 'muroplasts',^[9] 'cyanoplasts', or 'cyanelles'. Unlike the plastids in other organisms, they have a peptidoglycan layer, believed to be a relic of the endosymbiotic origin of plastids from cyanobacteria.^[1][10] Glaucophytes contain the photosynthetic pigment chlorophyll a.^[1] Along with red algae^[1] and cyanobacteria, they harvest light via phycobilisomes, structures consisting largely of phycobiliproteins. The green algae and land plants have lost that pigment.^[11] Like red algae, and in contrast to green algae and plants, glaucophytes store fixed carbon in the cytosol.^[12]

The most early-diverging genus is Cyanophora, which only has one or two plastids. When there are two, they are semi-connected.^[13]

Glaucophytes have mitochondria with flat cristae, and undergo open mitosis without centrioles. Motile forms have two unequal flagella, which may have fine hairs and are anchored by a multilayered system of microtubules, both of which are similar to forms found in some green algae.^[11]

Phylogeny

External

Together with red algae and Viridiplantae (green algae and land plants), glaucophytes form the Archaeplastida – a group of plastid-containing organisms that may share a unique common ancestor that established an endosymbiotic association with a cyanobacterium. The relationship among the three groups remains uncertain, although it is most likely that glaucophytes diverged first:^[4]

Archaeplastida	Glaucophyta Red algae Viridiplantae

The alternative, that glaucophytes and red algae form a clade, has been shown to be less plausible, but cannot be ruled out.^[4]

Internal

The internal phylogeny of the glaucophytes and the number of genera and species varies considerably among taxonomic sources. A phylogeny of the Glaucophyta published in 2017 divided the group into three families, and includes five genera:^[14]

Glaucophyta	Cyanophoraceae Cyanophora Gloeochaetaceae Cyanoptyche Gloeochaete Glaucocystidaceae Glaucocystopsis Glaucocystis

Taxonomy

A 2019 list of the described glaucophyte species has the same three subdivisions, treated as orders, but includes a further five unplaced possible species, producing a total of between 14 and 19 possible species.^[4]

• Order Cyanophorales
  • Genus Cyanophora – 5–6 species
• Order Glaucocystales
  • Genus Glaucocystis – 7–8 species
• Order Gloeochaetales
  • Cyanoptyche – 1 species
  • Gloeochaete – 1 species
• Other possible species
  • ?Archaeopsis monococca Skuja
  • ?Chalarodora azurea Pascher
  • ?Glaucocystopsis africana Bourrelly
  • ?Peliaina cyanea Pascher
  • ?Strobilomonas cyaneus Schiller

As of March 2022^[update], AlgaeBase divided glaucophytes into only two groups, placing Cyanophora in Glaucocystales rather than Cyanophorales (however the entry was dated 2011).^[15] AlgaeBase included a total of 26 species in nine genera:^[16]

• Glaucocystales
  • Chalarodora Pascher – 1 species
  • Corynoplastis Yokoyama, J.L.Scott, G.C.Zuccarello, M.Kajikawa, Y.Hara & J.A.West – 1 species
  • Cyanophora Korshikov – 6 species
  • Glaucocystis Itzigsohn – 13 species
  • Glaucocystopsis Bourrelly – 1 species
  • Peliaina Pascher – 1 species
  • Strobilomonas Schiller – 1 species
• Gloeochaetales
  • Cyanoptyche Pascher – 1 species
  • Gloeochaete Lagerheim – 1 species

None of the species of Glaucophyta is particularly common in nature.^[1]

The glaucophytes were considered before as part of family Oocystaceae, in the order Chlorococcales.^[17]

References

1. Keeling, Patrick J. (2004). "Diversity and evolutionary history of plastids and their hosts". American Journal of Botany. 91 (10): 1481–1493. doi:10.3732/ajb.91.10.1481. PMID 21652304.
2. Genomic Insights Into the Biology of Algae
3. Cruzan, Mitchell B. (2018). Evolutionary Biology. Oxford University Press. p. 20. ISBN 978-0-19-088268-6.
4. Figueroa-Martinez, Francisco; Jackson, Christopher; Reyes-Prieto, Adrian (2019). "Plastid Genomes from Diverse Glaucophyte Genera Reveal a Largely Conserved Gene Content and Limited Architectural Diversity". Genome Biology and Evolution. 11 (1): 174–188. doi:10.1093/gbe/evy268. PMC 6330054. PMID 30534986.
5. The monoplastidic bottleneck in algae and plant evolution | Journal of Cell Science
6. Guiry, M.D.; Guiry, G.M. "Glaucophyta". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-02-28.
7. Kim, Eunsoo; Graham, Linda E. (2008). Redfield, Rosemary Jeanne (ed.). "EEF2 Analysis Challenges the Monophyly of Archaeplastida and Chromalveolata". PLoS ONE. 3 (7): e2621. Bibcode:2008PLoSO...3.2621K. doi:10.1371/journal.pone.0002621. PMC 2440802. PMID 18612431.
8. Walker, Timothy (2012). Plants: A Very Short Introduction. Oxford University Press. p. 10. ISBN 978-0-19-958406-2.
9. Wise, Robert R.; Hoober, J. Kenneth, eds. (2006). The structure and function of plastids. Dordrecht: Springer. pp. 3–21. ISBN 978-1-4020-4061-0.
10. Miyagishima, Shin-ya; Kabeya, Yukihiro; Sugita, Chieko; Sugita, Mamoru; Fujiwara, Takayuki (2014). "DipM is required for peptidoglycan hydrolysis during chloroplast division". BMC Plant Biology. 14: 57. doi:10.1186/1471-2229-14-57. PMC 4015805. PMID 24602296.
11. Skuja, A. (1948). Taxonomie des Phytoplanktons einiger Seen in Uppland, Schweden. Symbolae Botanicae Upsalienses 9(3): 1-399.Guiry, M.D.; Guiry, G.M. "Glaucophyta". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.
12. Ball, S.; Colleoni, C.; Cenci, U.; Raj, J. N.; Tirtiaux, C. (10 January 2011). "The evolution of glycogen and starch metabolism in eukaryotes gives molecular clues to understand the establishment of plastid endosymbiosis". Journal of Experimental Botany. 62 (6): 1775–1801. doi:10.1093/jxb/erq411. PMID 21220783.
13. de Vries, Jan; Gould, Sven B. (2017-01-01). "The monoplastidic bottleneck in algae and plant evolution". Journal of Cell Science. 131 (2). The Company of Biologists. doi:10.1242/jcs.203414. ISSN 1477-9137. PMID 28893840.
14. Price, Dana C.; Steiner, Jürgen M.; Yoon, Hwan Su; Bhattacharya, Debashish; Löffelhardt, Wolfgang (2016). "Glaucophyta". Handbook of the Protists. pp. 1–65. doi:10.1007/978-3-319-32669-6_42-1. ISBN 978-3-319-32669-6.
15. Guiry, M.D.; Guiry, G.M. "Cyanophora". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-03-01.
16. Guiry, M.D.; Guiry, G.M. "Glaucophyta". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-03-01.
17. "Phycokey - Glaucocystis".