Glaucophyta
Parent authoritySkuja, 1954[1]
TaxonGlaucophyceae
AuthorityBohlin, 1901
Subdivision ranksOrders
Subdivision
SynonymsGlaucocystophyta Kies and Kremer, 1986

The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments,[2][3] less common today than they were during the Proterozoic.[4] The stated number of species in the group varies from about 14 to 26.[5][6][7] Together with the much larger sister taxa Rhodophyta (red algae) and Viridiplantae/Chloroplastida (green algae and land plants), they form the primary algae clade Archaeplastida.

The glaucophytes are of interest to biologists studying the evolution of chloroplasts as they may be similar to the ancestral algal type that led to the red algae and green plants, i.e. glaucophytes may be basal archaeplastids.[2][8][5]

Unlike red and green algae, glaucophytes only have asexual reproduction.[9]

Reproduction

Unlike red and green algae, glaucophytes reproduce exclusively through asexual means. They undergo open mitosis without centrioles, a trait shared with other basal eukaryotes. Reproductive modes include binary fission, zoospore formation, and autosporulation. For example, Cyanophora paradoxa divides longitudinally, producing two daughter cells, each inheriting a single cyanelle. Species of Glaucocystis reproduce via non-motile autospores. To date, there is no evidence of sexual reproduction in glaucophytes.[10]

Characteristics

The plastids of glaucophytes are known as 'muroplasts',[11] '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.[2][12] This peptidoglycan layer plays a functional role in plastid division and is considered molecular evidence of their cyanobacterial ancestry.[13] Glaucophytes contain the photosynthetic pigment chlorophyll a.[2] Along with red algae[2] and cyanobacteria, they harvest light via phycobilisomes, structures consisting largely of phycobiliproteins. The green algae and land plants have lost that pigment.[14] Like red algae, and in contrast to green algae and plants, glaucophytes store fixed carbon in the cytosol.[15]

This cytosolic carbon fixation, rather than fixation within plastids, is considered a retained ancestral trait. Glaucophyte phycobilisomes are composed primarily of phycocyanin and allophycocyanin, two key pigments also present in cyanobacteria. These pigments allow absorption of light at wavelengths that chlorophyll cannot, enhancing light harvesting in low-light aquatic environments.[16] Studies of endosymbiotic gene transfer (EGT) suggest that several genes originally encoded in cyanobacterial ancestors have been relocated to the nuclear genome in glaucophytes, reflecting early stages of plastid-host genomic integration.[17] The evolution of glycogen and starch metabolism in eukaryotes gives molecular clues to understand the establishment of plastid endosymbiosis.[citation needed]

The most early-diverging genus is Cyanophora, which only has one or two plastids. When there are two, they are semi-connected.[18]

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.[14]

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:[5]

The alternative, that glaucophytes and red algae form a clade, has been shown to be less plausible, but cannot be ruled out.[5]

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:[19]

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.[5]

As of May 2026, AlgaeBase divided glaucophytes into only two groups, placing Cyanophora in Glaucocystales rather than Cyanophorales (however the entry was dated 2011).[20] AlgaeBase included a total of 25 species in eight genera:[21]

  • Glaucocystales
    • Chalarodora Pascher – 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.[2]

The glaucophytes were considered before as part of family Oocystaceae, in the order Chlorococcales.[22]

References

  1. ^ Skuja, A. (1954). III. Abteilung: Glaucophyta. In: A. Engler's Syllabus der Pflanzenfamilien: mit besonderer Berücksichtigung der Nutzpflanzen nebst einer Übersicht über die Florenreiche und Florengebiete der Erde, 12th ed. I Band Allgemeiner Teil Bakterien bis Gymnospermen. (Melchior, H. & Werdermann, E. Eds), pp. 56–57. Berlin-Nikolassee: Borntraeger.
  2. ^ Keeling, Patrick J. (2004). "Diversity and evolutionary history of plastids and their hosts". American Journal of Botany. 91 (10): 1481–1493. Bibcode:2004AmJB...91.1481K. doi:10.3732/ajb.91.10.1481. PMID 21652304
  3. ^ Genomic Insights Into the Biology of Algae
  4. ^ Cruzan, Mitchell B. (2018). Evolutionary Biology. Oxford University Press. p. 20. ISBN 978-0-19-088268-6.
  5. ^ 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
  6. ^ The monoplastidic bottleneck in algae and plant evolution | Journal of Cell Science
  7. ^
  8. ^ Kim, Eunsoo & Graham, Linda E. (2008). "EEF2 Analysis Challenges the Monophyly of Archaeplastida and Chromalveolata". PLoS ONE. 3 (7). Bibcode:2008PLoSO...3.2621K. doi:10.1371/journal.pone.0002621. PMC 2440802. PMID 18612431
  9. ^ Walker, Timothy (2012). Plants: A Very Short Introduction. Oxford University Press. p. 10. ISBN 978-0-19-958406-2.
  10. ^ Jackson, C. (2015). The Glaucophyta: The blue-green plants in a nutshell. Acta Societatis Botanicorum Poloniae 84(4): 439–443. https://doi.org/10.5586/asbp.2015.049
  11. ^ The structure and function of plastids. Dordrecht: Springer. 2006. pp. 3–21. ISBN 978-1-4020-4061-0. Archived 2016-03-08 at the Wayback Machine. Retrieved 2019-03-12.
  12. ^ 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 (1): 57. Bibcode:2014BMCPB..14...57M. doi:10.1186/1471-2229-14-57. PMC 4015805. PMID 24602296
  13. ^ Oldach, Klaus H; Peck, David M; Nair, Ramakrishnan M; Sokolova, Maria; Harris, John; Bogacki, Paul; Ballard, Ross (2014). "Genetic analysis of tolerance to the root lesion nematode Pratylenchus neglectus in the legume Medicago littoralis". BMC Plant Biology. 14 (1): 100. Bibcode:2014BMCPB..14..100O. doi:10.1186/1471-2229-14-100. ISSN 1471-2229. PMC 4021308. PMID 24742262
  14. ^ Skuja, A. (1948). Taxonomie des Phytoplanktons einiger Seen in Uppland, Schweden. Symbolae Botanicae Upsalienses 9(3): 1-399.
  15. ^ 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
  16. ^ Ludwig-Müller, Jutta (2011-02-09). "Auxin conjugates: their role for plant development and in the evolution of land plants". Journal of Experimental Botany. 62 (6): 1757–1773. doi:10.1093/jxb/erq412. ISSN 1460-2431. PMID 21307383
  17. ^ Nowack, E. C. M., et al. (2008). Gene transfers from diverse bacteria compensate for reductive genome evolution in the chromatophore of Paulinella chromatophora. PNAS 105(5): 16782–16787. https://doi.org/10.1073/pnas.0809772105
  18. ^ 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
  19. ^ 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.
  20. ^
  21. ^
  22. ^ "Phycokey - Glaucocystis"