Rhizoplast

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Longitudinal section of the pelagophyte Plocamiomonas psychrophila under transmission electron microscopy showing system II fibre or rhizoplast (r) positioned at the base of the basal bodies and continuing parallel to the nucleus (N). The mature (mf) and immature (if) flagella are also visible. Plocamiomonas psychrophila Eur-J-Phycol fig34.jpg
Longitudinal section of the pelagophyte Plocamiomonas psychrophila under transmission electron microscopy showing system II fibre or rhizoplast (r) positioned at the base of the basal bodies and continuing parallel to the nucleus (N). The mature (mf) and immature (if) flagella are also visible.

The rhizoplast (also known as internal flagellar root, fibrous root or cross-banded root) [1] [2] [3] is an organelle present in a variety of flagellates, including ochrophyte and chlorophyte algae and some fungi. This term is used for a variety of striated, fibrous root-like structures that attach to the basal bodies (kinetosome) of the flagella and end in some other organelle. In the strictest sense, the term refers specifically to a type of root (known as system II fiber) that is composed of contractile microfibrils of centrin and connects directly to the surface of the cell nucleus.

Contents

Description

Rhizoplasts are organelles [4] that display a great diversity of structure and composition. They are components of the cytoskeleton as flagellar roots, closely related to the flagellar apparatus in many single-celled eukaryotic organisms that bear flagella (i.e., flagellates). [5] [6] There are two types of flagellar roots, both arising from the base of the flagella: the superficial root (also known as the microtubular root), which underlies the cell membrane, and the internal flagellar root or rhizoplast (also known as the fibrous root), which projects into the cell. [1] [2]

Rhizoplasts appear as striated, fibrous roots that are attached to the basal bodies (the structures from which flagella arise) at their proximal end, and develop in the direction of the cell nucleus. They are composed of protein microfibrils organized in rootlets, [6] but their exact proteic composition and structure varies from one group of organisms to another. [7] This great diversity is not known to be homologous; it is simply a synonym for any structure that appears as cross-banded or striated flagellar roots, which are commonly seen in flagellates. [8]

In the strictest sense, the term 'rhizoplast' only refers to those internal flagellar roots which connect directly to the surface of the nucleus. [9] These are alternatively known as basal body-nucleus connectors or system II fibers, and are found in some chlorophytes and most chromophyte families. These are composed of centrin proteins that assemble in contractile bundles of microfibrils, similar to muscle fibers; [8] these are capable of contraction modulated by calcium ions. In contrast, system I fibers, also commonly referred to as rhizoplasts, are composed of the non-contractile protein assemblin. [3]

Origin

The term 'rhizoplast' was first introduced by botanist Pierre Augustin Dangeard in 1901 through his comparative studies on zoospores and spermatozoids. He used the term to refer to a filamentous structure that connected the basal bodies and the cell nucleus, which he observed via light microscopy on the chloroplast-lacking alga Polytoma uvella . [1] [9] During the early 20th century, this observation lead to the popularized assumption that the flagellar apparatus was functionally connected to the nucleus in most flagellate cells. However, in the second half of the century this relationship was disproven for many species via electron microscopy studies: very often they end in some other unrelated structure, such as the pyrenoid or the cell membrane. [10] Only some select groups, such as some chlorophytes and many ochrophytes, maintain rhizoplasts as complex connectors between the nucleus and the basal bodies. [9] [3]

Occurrence

Fungi

Rhizoplasts are present in some zoospores of fungi. The chytrid genus Rhizophlyctis is characterized by the presence of a fibrous rhizoplast that directly links the nucleus with the kinetosome. It may play a role as a hinge during the redirection of movement. [11] [12] The aphelid species Aphelidium collabens has a striated rhizoplast that covers the anterior end of the kinetosome and ends near the posterior end of the nucleus. [13]

Function

There are many theories and speculations on the functionality of this union between the nucleus and the flagellar apparatus given by rhizoplasts, including: [8]

Related Research Articles

<span class="mw-page-title-main">Chlorophyta</span> Phylum of green algae

Chlorophyta is a division of green algae informally called chlorophytes.

<span class="mw-page-title-main">Flagellum</span> Cellular appendage functioning as locomotive or sensory organelle

A flagellum is a hairlike appendage that protrudes from certain plant and animal sperm cells, from fungal spores (zoospores), and from a wide range of microorganisms to provide motility. Many protists with flagella are known as flagellates.

<i>Chlamydomonas</i> Genus of algae

Chlamydomonas is a genus of green algae consisting of about 150 species of unicellular flagellates, found in stagnant water and on damp soil, in freshwater, seawater, and even in snow as "snow algae". Chlamydomonas is used as a model organism for molecular biology, especially studies of flagellar motility and chloroplast dynamics, biogenesis, and genetics. One of the many striking features of Chlamydomonas is that it contains ion channels (channelrhodopsins) that are directly activated by light. Some regulatory systems of Chlamydomonas are more complex than their homologs in Gymnosperms, with evolutionarily related regulatory proteins being larger and containing additional domains.

<i>Polytoma</i> Genus of algae

Polytoma is a genus of flagellates in the family Chlamydomonadaceae. Algae are similar to the genus Chlamydomonas, but lack chlorophyll and are colorless. Although they are not photosynthetic, they are grouped with the green algae because they are phylogenetically related to, and derived from, flagellate green algae.

<i>Tetraselmis</i> Genus of algae

Tetraselmis is a genus of phytoplankton. Tetraselmis is a green algal genus within the order Chlorodendrales, and they are characterized by their intensely-colored green chloroplast, their flagellated cell bodies, the presence of a pyrenoid within the chloroplast, and a scale-produced thecal-wall. Species within this genus are found in both marine and freshwater ecosystems across the globe; their habitat range is mainly limited by water depth due to their photosynthetic nature. Thus, they live in diverse water environments if enough nutrients and light are available for net photosynthetic activity. Tetraselmis species have proven to be useful for both research and industry. Tetraselmis species have been studied for understanding plankton growth rates, and recently a colonial species is being used to gain an understanding of multicellularity evolution. Additionally, many species are currently being examined for their use as biofuels due to their high lipid content.

<span class="mw-page-title-main">Chlorodendrales</span> Order of algae

Chlorodendrales are an order of green, flagellated, thecate, unicellular eukaryotes, within the green algae class Chlorodendrophyceae. Prasinophyceae are defined by their cellular scales which are composed of carbohydrates, and Chlorodendrales are unique within this group due to these scales forming a fused thecal wall. Cells of Chlorodendrales are completely covered in scales, which fuse around the cell body producing the theca, but remain individually separated on the flagella, of which there are typically four per cell. Species within Chlorodendrales live in both marine and fresh water habitats, occupying both benthic and planktonic food webs. Additionally, they are photoautotrophs, meaning they produce their own food through the conversion of sunlight into chemical energy.

<i>Carteria</i> Genus of algae

Carteria is a genus of green algae in the family Chlamydomonadaceae. Carteria are similar in morphology to the common genus Chlamydomonas and differ by having four, rather than two, flagella at the vegetative stage.

<i>Nephroselmis</i> Genus of algae

Nephroselmis is a genus of green algae. It has been placed in the family Nephroselmidaceae, although a 2009 study suggests that it should be separated into its own class, Nephroselmidophyceae. One species can be an endosymbiont of Hatena arenicola.

<span class="mw-page-title-main">Centrin</span> Family of calcium-binding phosphoproteins

Centrins, also known as caltractins, are a family of calcium-binding phosphoproteins found in the centrosome of eukaryotes. Centrins are small calcium binding proteins that are ubiquitous centrosome components. There are about 350 “signature” proteins that are unique to eukaryotic cells but have no significant homology to proteins in archaea and bacteria. They are a type of protein that is essential and present in almost all eukaryotic cells and are found in the centrioles and pericentriolar lattice. Human centrin genes are CETN1, CETN2 and CETN3.

<i>Proteromonas</i> Genus of single-celled organisms

Proteromonas is a genus of single-celled biflagellated microbial eukaryotes belonging to the Superphylum Stramenopiles which are characterized by the presence of tripartite, hair-like structures on the anteriorly-directed larger of the two flagella. Proteromonas on the other hand are notable by having tripartite hairs called somatonemes not on the flagella but on the posterior of the cell. Proteromonas are closely related to Karotomorpha and Blastocystis, which belong to the Opalines group.

Psalteriomonas is a genus of excavates in the group of Heterolobosea. The genus was first discovered and named in 1990. It contains amoeboflagellate cells that live in freshwater anaerobic sediments all over the world. The microtubule-organizing ribbon and the associated microfibrillar bundles of the mastigote system is the predominant feature in Psalteriomonas. This harp-shaped complex gives rise to the name of this genus. Psalteriomonasforms an endosymbiotic relationship with methanogenic bacteria, especially with Methanobacterium formicicum There are currently three species in this genus: P. lanterna, P. vulgaris, and P. magna.

Oxymonas is a genus of Excavata.

<i>Collodictyon</i> Genus of algae

Collodictyon is a genus of single-celled, omnivorous eukaryotes belonging to the collodictyonids, also known as diphylleids. Due to their mix of cellular components, Collodictyonids do not belong to any well-known kingdom-level grouping of that domain and this makes them distinctive from other families. Recent research places them in a new 'supergroup' together with rigifilids and Mantamonas, with the so-far informal name 'CRuMs'.

Michael Melkonian is a German botanist and professor of botany at the University of Cologne.

<span class="mw-page-title-main">Protist locomotion</span> Motion system of a type of eukaryotic organism

Protists are the eukaryotes that cannot be classified as plants, fungi or animals. They are mostly unicellular and microscopic. Many unicellular protists, particularly protozoans, are motile and can generate movement using flagella, cilia or pseudopods. Cells which use flagella for movement are usually referred to as flagellates, cells which use cilia are usually referred to as ciliates, and cells which use pseudopods are usually referred to as amoeba or amoeboids. Other protists are not motile, and consequently have no built-in movement mechanism.

Holomastigotoides is a genus of parabasalids found in the hindgut of lower termites. It is characterized by its dense, organized arrangement of flagella on the cell surface and the presence of a mitotic spindle outside its nucleus during the majority of its cell cycle. As a symbiont of termites, Holomastigotoides is able to ingest wood and aid its host in digestion. In return, Holomastigotoides is supplied with a stable habitat and steady supply of food. Holomastigotoides has notably been studied to observe the mechanisms of chromosomal pairing and segregation in haploid and diploid cells.

<span class="mw-page-title-main">Ultrastructural identity</span>

Ultrastructural identity is a concept in biology. It asserts that evolutionary lineages of eukaryotes in general and protists in particular can be distinguished by complements and arrangements of cellular organelles. These ultrastructural components can be visualized by electron microscopy.

<span class="mw-page-title-main">Glissomonadida</span> Order of protists

The glissomonads are a group of bacterivorous gliding flagellated protists that compose the order Glissomonadida, in the amoeboflagellate phylum Cercozoa. They comprise a vast, largely undescribed diversity of soil and freshwater organisms. They are the sister group to cercomonads; the two orders form a solid clade of gliding soil-dwelling flagellates called Pediglissa.

<span class="mw-page-title-main">Viridiraptoridae</span> Family of predatorial protists

Viridiraptoridae, previously known as clade X, is a clade of heterotrophic protists in the phylum Cercozoa. They're a family of glissomonads, a group containing a vast, mostly undescribed diversity of soil and freshwater organisms.

<i>Olisthodiscus</i> Class of heterokont algae

Olisthodiscus is a genus of heterokont algae, present in marine or brackish waters. It is the only genus in the family Olisthodiscaceae, the order Olisthodiscales, and the class Olisthodiscophyceae. After a long history of controversial classifications, in 2021 it was recognized as a phylogenetically distinct lineage from the rest of ochrophyte classes.

References

Citations

  1. 1 2 3 Moestrup 1982, p. 493.
  2. 1 2 Andersen 1991, p. 149.
  3. 1 2 3 Brugerolle & Mignot 2003, p. 13.
  4. ↑ Salisbury et al. 1984, p. 962.
  5. ↑ Brugerolle & Mignot 1990, p. 248.
  6. 1 2 Brugerolle & Mignot 2003, p. 17.
  7. 1 2 3 Brugerolle & Mignot 2003, p. 20.
  8. 1 2 3 4 5 Moestrup 1982, p. 495.
  9. 1 2 3 Melkonian et al. 1992, p. 184.
  10. ↑ Moestrup 1982, p. 494.
  11. ↑ Lechter et al. 2008, p. 1035.
  12. ↑ Galindo, Richards & Nirody 2024.
  13. ↑ Seto et al. 2020, p. 5.
  14. 1 2 Moestrup 1982, p. 496.
  15. ↑ Boyd et al. 2011.

Cited literature

  • Andersen, R. A. (1991). "The cytoskeleton of chromophyte algae". Protoplasma. 164 (1–3): 143–159. doi:10.1007/BF01320820.
  • Boyd, Joseph S.; Gray, Miranda M.; Thompson, Mark D.; Horst, Cynthia J.; Dieckmann, Carol L. (2011). "The daughter four-membered microtubule rootlet determines anterior–posterior positioning of the eyespot in Chlamydomonas reinhardtii". Cytoskeleton. 68: 459–469. doi:10.1002/cm.20524.
  • Brugerolle, G.; Mignot, J.-P. (2003). "The rhizoplast of chrysomonads, a basal body–nucleus connector that polarises the dividing spindle". Protoplasma. 222 (1–2): 13–21. doi:10.1007/s00709-003-0016-4. PMID   14513307.
  • Galindo, Luis Javier; Richards, Thomas A.; Nirody, Jasmine A. (11 September 2024). "Evolutionarily diverse fungal zoospores show contrasting swimming patterns specific to ultrastructure". Current Biology. doi:10.1016/j.cub.2024.08.016.
  • Lechter, Peter M.; Powell, Martha J.; Barr, Donald J.S.; Churchill, Perry F.; Wakefield, William S.; Picard, Kathryn T. (September 2008). "Rhizophlyctidales—a new order in Chytridiomycota". Mycological Research. 112 (9): 1031–1048. doi:10.1016/j.mycres.2008.03.007. PMID   18701267.
  • Brugerolle, G.; Mignot, J. P. (1990). "Proteromonadida". In Margulis, Lynn; Corliss, John O.; Melkonian, Michael; Chapman, David J. (eds.). Handbook of Protoctista: the structure, cultivation, habitats and life histories of the eukaryotic microorganisms and their descendants exclusive of animals, plants and fungi. A guide to the algae, ciliates, foraminifera, sporozoa, water molds, slime molds, and the other protoctists. Boston: Jones and Bartlett publishers. pp. 246–251. ISBN   0-86720-052-9.
  • Melkonian, Michael; Beech, Peter L.; Katsaros, Christos; Schulze, Dorothee (1992). "Centrin-Mediated Cell Motility in Algae". In Melkonian, Michael (ed.). Algal Cell Motility. Boston, MA: Springer. pp. 179–221. doi:10.1007/978-1-4615-9683-7_6. ISBN   978-1-4615-9683-7.
  • Moestrup, Øjvind (1982). "Phycological Reviews 7. Flagellar structure in algae: a review, with new observations particularly on the Chrysophyceae, Phaeophyceae (Fucophyceae), Euglenophyceae and Reckertia". Phycologia. 21 (4): 427–528. doi:10.2216/i0031-8884-21-4-427.1.
  • Salisbury, J. L.; Baron, A.; Surek, Barbara; Melkonian, M. (1 September 1984). "Striated flagellar roots: isolation and partial characterization of a calcium-modulated contractile organelle" (PDF). Journal of Cell Biology. 99 (3): 962–970. doi: 10.1083/jcb.99.3.962 . PMC   2113404 . PMID   6381510.
  • Seto, Kensuke; Matsuzawa, Toshihiro; Kuno, Hitoshi; Kagami, Maiko (19 May 2020). "Morphology, ultrastructure, and molecular phylogeny of Aphelidium collabens sp. nov. (Aphelida), a parasitoid of a green alga Coccomyxa sp". Protist. 171 (3): 125728. doi:10.1016/j.protis.2020.125728. PMID   32544843.
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