Prasinophyte Paraphyletic group of chlorophytes
| |
---|---|
Pyramimonas sp. | |
Scientific classification | |
(unranked): | Viridiplantae |
Division: | Chlorophyta |
Informal group: | Prasinophyte |
Included classes [1] [2] | |
Excluded classes (i.e. chlorophytes not considered prasinophytes) | |
The prasinophytes are a group of unicellular green algae. [3] Prasinophytes mainly include marine planktonic species, as well as some freshwater representatives. [3] [4] 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. [4] Well studied genera include Ostreococcus, considered to be the smallest (ca. 0.95 μm) free-living eukaryote, [5] and Micromonas, both of which are found in marine waters worldwide. 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 [6] [7] and 21 Mbp for Micromonas [8]). At least one species, the Antarctic form Pyramimonas gelidicola, is capable of phagocytosis and is therefore a mixotrophic algae. [9]
Some authors treat the prasinophytes as a polyphyletic grouping of green algae from different clades. As the Tetraphytina emerged in the Prasinophytes, recently authors include it, rendering it monophyletic, and equivalent to chlorophyta. [10] [11]
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) [12] and several different ecotypes of Ostreococcus have been detected in the environment. [13] 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 [14] and observed year-round in the coastal North Pacific Ocean. [15] 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. [16] 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. [17]
Prasinophytes are subject to infection by large double-stranded DNA viruses belonging to the genus Prasinovirus in the family Phycodnaviridae, [18] [19] [20] as well as a Reovirus. [21] It has been estimated that from 2 to 10% of the Micromonas pusilla population is lysed per day by viruses. [22]
Recent studies agree that the prasinophytes are not a natural group, being highly paraphyletic. [4] [23] [24] [25] Relationships among the groups making up the Chlorophyta are not fully resolved. The cladogram produced by Leliaert et al. 2011 [4] and some modification according to Silar 2016, [26] Leliaert 2016 [27] and Lopes dos Santos et al. 2017 [1] is shown below. The blue shaded groups are or have traditionally been placed in the Prasinophyceae [3]). The species Mesostigma viride has been shown to be a member of the Streptophyta or basal Green algae. The others are member of the Chlorophyta.
Green Algae |
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
As 2020 paper places the Palmophyllophyceae (prasinophyte clade VI) in a new phylum outside of the Chlorophyta and Streptophyta, the Prasinodermophyta. [28]
Prasinophyte Paraphyletic group of chlorophytes
| |
---|---|
Pyramimonas sp. | |
Scientific classification | |
(unranked): | Viridiplantae |
Division: | Chlorophyta |
Informal group: | Prasinophyte |
Included classes [1] [2] | |
Excluded classes (i.e. chlorophytes not considered prasinophytes) | |
The prasinophytes are a group of unicellular green algae. [3] Prasinophytes mainly include marine planktonic species, as well as some freshwater representatives. [3] [4] 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. [4] Well studied genera include Ostreococcus, considered to be the smallest (ca. 0.95 μm) free-living eukaryote, [5] and Micromonas, both of which are found in marine waters worldwide. 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 [6] [7] and 21 Mbp for Micromonas [8]). At least one species, the Antarctic form Pyramimonas gelidicola, is capable of phagocytosis and is therefore a mixotrophic algae. [9]
Some authors treat the prasinophytes as a polyphyletic grouping of green algae from different clades. As the Tetraphytina emerged in the Prasinophytes, recently authors include it, rendering it monophyletic, and equivalent to chlorophyta. [10] [11]
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) [12] and several different ecotypes of Ostreococcus have been detected in the environment. [13] 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 [14] and observed year-round in the coastal North Pacific Ocean. [15] 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. [16] 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. [17]
Prasinophytes are subject to infection by large double-stranded DNA viruses belonging to the genus Prasinovirus in the family Phycodnaviridae, [18] [19] [20] as well as a Reovirus. [21] It has been estimated that from 2 to 10% of the Micromonas pusilla population is lysed per day by viruses. [22]
Recent studies agree that the prasinophytes are not a natural group, being highly paraphyletic. [4] [23] [24] [25] Relationships among the groups making up the Chlorophyta are not fully resolved. The cladogram produced by Leliaert et al. 2011 [4] and some modification according to Silar 2016, [26] Leliaert 2016 [27] and Lopes dos Santos et al. 2017 [1] is shown below. The blue shaded groups are or have traditionally been placed in the Prasinophyceae [3]). The species Mesostigma viride has been shown to be a member of the Streptophyta or basal Green algae. The others are member of the Chlorophyta.
Green Algae |
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
As 2020 paper places the Palmophyllophyceae (prasinophyte clade VI) in a new phylum outside of the Chlorophyta and Streptophyta, the Prasinodermophyta. [28]