62-397: See text Charales is an order of freshwater green algae in the division Charophyta , class Charophyceae , commonly known as stoneworts . Depending on the treatment of the genus Nitellopsis , living (extant) species are placed into either one family ( Characeae ) or two (Characeae and Feistiellaceae ). Further families are used for fossil members of the order. Linnaeus established
124-419: A complicated feeding apparatus that feeds on other microbes. When it engulfs a green Nephroselmis alga, the feeding apparatus disappears and it becomes photosynthetic. During mitosis the algae is transferred to only one of the daughter cells, while the other cell restarts the cycle. In 1966, biologist Kwang W. Jeon found that a lab strain of Amoeba proteus had been infected by bacteria that lived inside
186-414: A group of photosynthetic, eukaryotic organisms that include species with haplobiontic and diplobiontic life cycles. The diplobiontic species, such as Ulva , follow a reproductive cycle called alternation of generations in which two multicellular forms, haploid and diploid, alternate, and these may or may not be isomorphic (having the same morphology). In haplobiontic species only the haploid generation,
248-412: A lineage of amoeba in the genus Paulinella independently engulfed a cyanobacteria that evolved to be functionally synonymous with traditional chloroplasts, called chromatophores. Some 100 million years ago, UCYN-A, a nitrogen-fixing bacterium, became an endosymbiont of the marine alga Braarudosphaera bigelowii , eventually evolving into a nitroplast , which fixes nitrogen. Similarly, diatoms in
310-463: A multicellular gametophyte. All land plants have a diplobiontic common ancestor, and diplobiontic forms have also evolved independently within Ulvophyceae more than once (as has also occurred in the red and brown algae). Diplobiontic green algae include isomorphic and heteromorphic forms. In isomorphic algae, the morphology is identical in the haploid and diploid generations. In heteromorphic algae,
372-507: A step that occurred in the evolution of organelles (above). Mixotricha paradoxa is a protozoan that lacks mitochondria. However, spherical bacteria live inside the cell and serve the function of the mitochondria. Mixotricha has three other species of symbionts that live on the surface of the cell. Paramecium bursaria , a species of ciliate , has a mutualistic symbiotic relationship with green alga called Zoochlorella . The algae live in its cytoplasm. Platyophrya chlorelligera
434-402: A tsetse fly symbiont, is vertically transmitted (via mother's milk). When a symbiont reaches this stage, it resembles a cellular organelle , similar to mitochondria or chloroplasts . In vertical transmission , the symbionts do not need to survive independently, often leading them to have a reduced genome. For instance, pea aphid symbionts have lost genes for essential molecules and rely on
496-496: Is a freshwater ciliate that harbors Chlorella that perform photosynthesis. Strombidium purpureum is a marine ciliate that uses endosymbiotic, purple, non-sulphur bacteria for anoxygenic photosynthesis. Paulinella chromatophora is a freshwater amoeboid that has a cyanobacterium endosymbiont. Many foraminifera are hosts to several types of algae, such as red algae , diatoms , dinoflagellates and chlorophyta . These endosymbionts can be transmitted vertically to
558-468: Is a unicellular, isogamous charophycean alga group that is the closest unicellular relative to land plants. Heterothallic strains of different mating type can conjugate to form zygospores . Sex pheromones termed protoplast-release inducing proteins (glycopolypeptides) produced by mating-type (-) and mating-type (+) cells facilitate this process. The green algae, including the characean algae, have served as model experimental organisms to understand
620-564: Is episodic (when the cicadas reproduce). The original Hodgkinia genome split into three much simpler endosymbionts, each encoding only a few genes—an instance of punctuated equilibrium producing distinct lineages. The host requires all three symbionts. Symbiont transmission is the process where the host acquires its symbiont. Since symbionts are not produced by host cells, they must find their own way to reproduce and populate daughter cells as host cells divide. Horizontal, vertical, and mixed-mode (hybrid of horizonal and vertical) transmission are
682-595: Is known of the nature of the association (mode of infection, transmission, metabolic requirements, etc.) but phylogenetic analysis indicates that these symbionts belong to the class Alphaproteobacteria , relating them to Rhizobium and Thiobacillus . Other studies indicate that these subcuticular bacteria may be both abundant within their hosts and widely distributed among the Echinoderms. Some marine oligochaeta (e.g., Olavius algarvensis and Inanidrillus spp. ) have obligate extracellular endosymbionts that fill
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#1732851167091744-458: Is mediated by toxins called " ribosome -inactivating proteins " that attack the molecular machinery of invading parasites. These toxins represent one of the first understood examples of a defensive symbiosis with a mechanistic understanding for defensive symbiosis between an insect endosymbiont and its host. Sodalis glossinidius is a secondary endosymbiont of tsetse flies that lives inter- and intracellularly in various host tissues, including
806-637: Is not obligatory, especially in nitrogen-replete areas. Richelia intracellularis is also found in Rhizosolenia spp., a diatom found in oligotrophic oceans. Compared to the Hemaiulus host, the endosymbiosis with Rhizosolenia is much more consistent, and Richelia intracellularis is generally found in Rhizosolenia . There are some asymbiotic (occurs without an endosymbiont) Rhizosolenia, however there appears to be mechanisms limiting growth of these organisms in low nutrient conditions. Cell division for both
868-433: The (green) plants (with chloroplasts ) the red algae (with rhodoplasts) and the glaucophytes (with muroplasts). Green algae are often classified with their embryophyte descendants in the green plant clade Viridiplantae (or Chlorobionta ). Viridiplantae, together with red algae and glaucophyte algae, form the supergroup Primoplantae, also known as Archaeplastida or Plantae sensu lato . The ancestral green alga
930-500: The Calothrix genome is generally intact. While other species like that of the UNCY-A symbiont and Richelia have reduced genomes. This reduction in genome size occurs within nitrogen metabolism pathways indicating endosymbiont species are generating nitrogen for their hosts and losing the ability to use this nitrogen independently. This endosymbiont reduction in genome size, might be
992-622: The Chlorophyta and Charophyta / Streptophyta . The land plants ( Embryophytes ) have emerged deep in the Charophyte alga as a sister of the Zygnematophyceae . Since the realization that the Embryophytes emerged within the green algae, some authors are starting to include them. The completed clade that includes both green algae and embryophytes is monophyletic and is referred to as
1054-478: The Greek : ἔνδον endon "within", σύν syn "together" and βίωσις biosis "living". Symbiogenesis theory holds that eukaryotes evolved via absorbing prokaryotes . Typically, one organism envelopes a bacterium and the two evolve a mutualistic relationship. The absorbed bacteria (the endosymbiont) eventually lives exclusively within the host cells. This fits the concept of observed organelle development. Typically
1116-497: The gametophyte is multicellular. The fertilized egg cell, the diploid zygote , undergoes meiosis , giving rise to haploid cells which will become new gametophytes. The diplobiontic forms, which evolved from haplobiontic ancestors, have both a multicellular haploid generation and a multicellular diploid generation. Here the zygote divides repeatedly by mitosis and grows into a multicellular diploid sporophyte . The sporophyte produces haploid spores by meiosis that germinate to produce
1178-453: The hemolymph of the insects (not specialized bacteriocytes, see below), and are not obligate. Among primary endosymbionts of insects, the best-studied are the pea aphid ( Acyrthosiphon pisum ) and its endosymbiont Buchnera sp. APS, the tsetse fly Glossina morsitans morsitans and its endosymbiont Wigglesworthia glossinidia brevipalpis and the endosymbiotic protists in lower termites . As with endosymbiosis in other insects,
1240-641: The root nodules of legumes , single-cell algae inside reef-building corals , and bacterial endosymbionts that provide essential nutrients to insects . Endosymbiosis played key roles in the development of eukaryotes and plants. Roughly 2.2 billion years ago an archaeon absorbed a bacterium through phagocytosis , that eventually became the mitochondria that provide energy to almost all living eukaryotic cells. Approximately 1 billion years ago, some of those cells absorbed cyanobacteria that eventually became chloroplasts , organelles that produce energy from sunlight. Approximately 100 million years ago,
1302-502: The supralittoral zone , is terrestrial and can in the Antarctic form large carpets on humid soil, especially near bird colonies. Green algae have chloroplasts that contain chlorophyll a and b , giving them a bright green colour, as well as the accessory pigments beta carotene (red-orange) and xanthophylls (yellow) in stacked thylakoids . The cell walls of green algae usually contain cellulose , and they store carbohydrate in
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#17328511670911364-643: The Charales is Eochara wickendenii Choquette from the Middle Devonian. The family Characeae starts dominating the fossil assemblages in the Paleogene or perhaps already in the Late Cretaceous . Green algae The green algae ( sg. : green alga ) are a group of chlorophyll -containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains
1426-708: The Mesostigmatophyceae, Chlorokybophyceae and spirotaenia are only more conventionally basal Streptophytes. The algae of this paraphyletic group "Charophyta" were previously included in Chlorophyta, so green algae and Chlorophyta in this definition were synonyms. As the green algae clades get further resolved, the embryophytes, which are a deep charophyte branch, are included in " algae ", "green algae" and " Charophytes ", or these terms are replaced by cladistic terminology such as Archaeplastida , Plantae / Viridiplantae , and streptophytes , respectively. Green algae are
1488-552: The algae's chloroplasts. These chloroplasts retain their photosynthetic capabilities and structures for several months after entering the slug's cells. Trichoplax have two bacterial endosymbionts. Ruthmannia lives inside the animal's digestive cells. Grellia lives permanently inside the endoplasmic reticulum (ER), the first known symbiont to do so. Paracatenula is a flatworm which have lived in symbiosis with an endosymbiotic bacteria for 500 million years. The bacteria produce numerous small, droplet-like vesicles that provide
1550-405: The assumption hat primary endosymbionts are transferred only vertically. Attacking obligate bacterial endosymbionts may present a way to control their hosts, many of which are pests or human disease carriers. For example, aphids are crop pests and the tsetse fly carries the organism Trypanosoma brucei that causes African sleeping sickness . Studying insect endosymbionts can aid understanding
1612-477: The bacteria are transmitted in the egg , as in Buchnera ; in others like Wigglesworthia , they are transmitted via milk to the embryo. In termites, the endosymbionts reside within the hindguts and are transmitted through trophallaxis among colony members. Primary endosymbionts are thought to help the host either by providing essential nutrients or by metabolizing insect waste products into safer forms. For example,
1674-611: The clade Viridiplantae and as the kingdom Plantae . The green algae include unicellular and colonial flagellates , most with two flagella per cell, as well as various colonial, coccoid (spherical), and filamentous forms, and macroscopic, multicellular seaweeds . There are about 22,000 species of green algae, many of which live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds. A few other organisms rely on green algae to conduct photosynthesis for them. The chloroplasts in dinoflagellates of
1736-413: The class Chlorophyceae undergo closed mitosis in the most common form of cell division among the green algae, which occurs via a phycoplast . By contrast, charophyte green algae and land plants (embryophytes) undergo open mitosis without centrioles . Instead, a 'raft' of microtubules, the phragmoplast , is formed from the mitotic spindle and cell division involves the use of this phragmoplast in
1798-680: The cyanobacterium Richelia intracellularis has been reported in North Atlantic, Mediterranean, and Pacific waters. Richelia is found within the diatom frustule of Hemiaulus spp., and has a reduced genome. A 2011 study measured nitrogen fixation by the cyanobacterial host Richelia intracellularis well above intracellular requirements, and found the cyanobacterium was likely fixing nitrogen for its host. Additionally, both host and symbiont cell growth were much greater than free-living Richelia intracellularis or symbiont-free Hemiaulus spp. The Hemaiulus - Richelia symbiosis
1860-1285: The cytoplasmic vacuoles . This infection killed almost all of the infected protists. After the equivalent of 40 host generations, the two organisms become mutually interdependent. A genetic exchange between the prokaryotes and protists occurred. The spotted salamander ( Ambystoma maculatum ) lives in a relationship with the algae Oophila amblystomatis , which grows in its egg cases. All vascular plants harbor endosymbionts or endophytes in this context. They include bacteria , fungi , viruses , protozoa and even microalgae . Endophytes aid in processes such as growth and development, nutrient uptake, and defense against biotic and abiotic stresses like drought , salinity , heat, and herbivores. Plant symbionts can be categorized into epiphytic , endophytic , and mycorrhizal . These relations can also be categorized as beneficial, mutualistic , neutral, and pathogenic . Microorganisms living as endosymbionts in plants can enhance their host's primary productivity either by producing or capturing important resources. These endosymbionts can also enhance plant productivity by producing toxic metabolites that aid plant defenses against herbivores . Plants are dependent on plastid or chloroplast organelles. The chloroplast
1922-464: The diatom host and cyanobacterial symbiont can be uncoupled and mechanisms for passing bacterial symbionts to daughter cells during cell division are still relatively unknown. Other endosymbiosis with nitrogen fixers in open oceans include Calothrix in Chaetoceros spp. and UNCY-A in prymnesiophyte microalga. The Chaetoceros - Calothrix endosymbiosis is hypothesized to be more recent, as
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1984-469: The endosymbiont's genome shrinks, discarding genes whose roles are displaced by the host. For example, the Hodgkinia genome of Magicicada cicadas is much different from the prior freestanding bacteria. The cicada life cycle involves years of stasis underground. The symbiont produces many generations during this phase, experiencing little selection pressure , allowing their genomes to diversify. Selection
2046-430: The entire body of their host. These marine worms are nutritionally dependent on their symbiotic chemoautotrophic bacteria lacking any digestive or excretory system (no gut, mouth, or nephridia ). The sea slug Elysia chlorotica 's endosymbiont is the algae Vaucheria litorea . The jellyfish Mastigias have a similar relationship with an algae. Elysia chlorotica forms this relationship intracellularly with
2108-403: The environment of the host insect cell. A complementary theory suggests that the relatively small numbers of bacteria inside each insect decrease the efficiency of natural selection in 'purging' deleterious mutations and small mutations from the population, resulting in a loss of genes over many millions of years. Research in which a parallel phylogeny of bacteria and insects was inferred supports
2170-729: The family Rhopalodiaceae have cyanobacterial endosymbionts, called spheroid bodies or diazoplasts, which have been proposed to be in the early stages of organelle evolution. Symbionts are either obligate (require their host to survive) or facultative (can survive independently). The most common examples of obligate endosymbiosis are mitochondria and chloroplasts , which reproduce via mitosis in tandem with their host cells. Some human parasites, e.g. Wuchereria bancrofti and Mansonella perstans , thrive in their intermediate insect hosts because of an obligate endosymbiosis with Wolbachia spp. They can both be eliminated by treatments that target their bacterial host. Endosymbiosis comes from
2232-427: The form of starch . All green algae have mitochondria with flat cristae . When present, paired flagella are used to move the cell. They are anchored by a cross-shaped system of microtubules and fibrous strands. Flagella are only present in the motile male gametes of charophytes bryophytes, pteridophytes, cycads and Ginkgo , but are absent from the gametes of Pinophyta and flowering plants . Members of
2294-435: The fungal species that partner in lichens cannot live on their own, while the algal species is often found living in nature without the fungus. Trentepohlia is a filamentous green alga that can live independently on humid soil, rocks or tree bark or form the photosymbiont in lichens of the family Graphidaceae . Also the macroalga Prasiola calophylla (Trebouxiophyceae) is terrestrial, and Prasiola crispa , which live in
2356-458: The genus Chara in 1753. The higher level classification of green algae was unsettled as of February 2022. AlgaeBase places Charales within the class Charophyceae and its circumscription of the division Charophyta . The number of families and their division into genera varies. As of February 2022, AlgaeBase accepts two families containing some extant species and four families containing only fossil species: AlgaeBase places
2418-580: The genus Lepidodinium , euglenids and chlorarachniophytes were acquired from ingested endosymbiont green algae, and in the latter retain a nucleomorph (vestigial nucleus). Green algae are also found symbiotically in the ciliate Paramecium , and in Hydra viridissima and in flatworms . Some species of green algae, particularly of genera Trebouxia of the class Trebouxiophyceae and Trentepohlia (class Ulvophyceae ), can be found in symbiotic associations with fungi to form lichens . In general
2480-401: The genus Nitellopsis , which has both extant and extinct species, in the family Feistiellaceae . Other sources place Nitellopsis in the family Characeae, with Feistiellaceae containing only fossil species, so that all extant species are in the family Characeae. The Interim Register of Marine and Nonmarine Genera accepts a further three extinct families: Body fossils of representatives of
2542-402: The heat of late summer. As their environment dries out, asexual V. carteri quickly die. However, they are able to escape death by switching, shortly before drying is complete, to the sexual phase of their life cycle that leads to production of dormant desiccation-resistant zygotes . Sexual development is initiated by a glycoprotein pheromone (Hallmann et al., 1998). This pheromone is one of
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2604-541: The host requires a specific Symbiodinium clade . More often, however, the distribution is ecological, with symbionts switching among hosts with ease. When reefs become environmentally stressed, this distribution is related to the observed pattern of coral bleaching and recovery. Thus, the distribution of Symbiodinium on coral reefs and its role in coral bleaching is an important in coral reef ecology. In marine environments, endosymbiont relationships are especially prevalent in oligotrophic or nutrient-poor regions of
2666-1148: The host to supply them. In return, the symbionts synthesize essential amino acids for the aphid host. When a symbiont reaches this stage, it begins to resemble a cellular organelle , similar to mitochondria or chloroplasts . Such dependent hosts and symbionts form a holobiont . In the event of a bottleneck, a decrease in symbiont diversity could compromise host-symbiont interactions, as deleterious mutations accumulate. The best-studied examples of endosymbiosis are in invertebrates . These symbioses affect organisms with global impact, including Symbiodinium (corals), or Wolbachia (insects). Many insect agricultural pests and human disease vectors have intimate relationships with primary endosymbionts. Scientists classify insect endosymbionts as Primary or Secondary. Primary endosymbionts (P-endosymbionts) have been associated with their insect hosts for millions of years (from ten to several hundred million years). They form obligate associations and display cospeciation with their insect hosts. Secondary endosymbionts more recently associated with their hosts, may be horizontally transferred, live in
2728-588: The host with needed nutrients. Dinoflagellate endosymbionts of the genus Symbiodinium , commonly known as zooxanthellae , are found in corals , mollusks (esp. giant clams , the Tridacna ), sponges , and the unicellular foraminifera . These endosymbionts capture sunlight and provide their hosts with energy via carbonate deposition. Previously thought to be a single species, molecular phylogenetic evidence reported diversity in Symbiodinium . In some cases,
2790-401: The insect's immune response. One of the best-understood defensive symbionts is the spiral bacteria Spiroplasma poulsonii . Spiroplasma sp. can be reproductive manipulators, but also defensive symbionts of Drosophila flies. In Drosophila neotestacea , S. poulsonii has spread across North America owing to its ability to defend its fly host against nematode parasites. This defence
2852-409: The legume host, which causes the rhizobia species (endosymbiont) to activate its Nod genes. These Nod genes generate lipooligosaccharide signals that the legume detects, leading to root nodule formation. This process bleeds into other processes such as nitrogen fixation in plants. The evolutionary advantage of such an interaction allows genetic exchange between both organisms involved to increase
2914-511: The light microscope. This process is called conjugation and occurs for example in Spirogyra . Sex pheromone production is likely a common feature of green algae, although only studied in detail in a few model organisms. Volvox is a genus of chlorophytes . Different species form spherical colonies of up to 50,000 cells. One well-studied species, Volvox carteri (2,000 – 6,000 cells) occupies temporary pools of water that tend to dry out in
2976-464: The mechanisms of the ionic and water permeability of membranes, osmoregulation , turgor regulation, salt tolerance , cytoplasmic streaming , and the generation of action potentials . Endosymbiont An endosymbiont or endobiont is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia ), which live in
3038-421: The midgut and hemolymph. Phylogenetic studies do not report a correlation between evolution of Sodalis and tsetse. Unlike Wigglesworthia, Sodalis has been cultured in vitro . Cardinium and m any other insects have secondary endosymbionts. Extracellular endosymbionts are represented in all four extant classes of Echinodermata ( Crinoidea , Ophiuroidea , Echinoidea , and Holothuroidea ). Little
3100-587: The morphology and size are different in the gametophyte and sporophyte. Reproduction varies from fusion of identical cells ( isogamy ) to fertilization of a large non-motile cell by a smaller motile one ( oogamy ). However, these traits show some variation, most notably among the basal green algae called prasinophytes . Haploid algal cells (containing only one copy of their DNA) can fuse with other haploid cells to form diploid zygotes. When filamentous algae do this, they form bridges between cells, and leave empty cell walls behind that can be easily distinguished under
3162-417: The most potent known biological effector molecules. It can trigger sexual development at concentrations as low as 10 M. Kirk and Kirk showed that sex-inducing pheromone production can be triggered experimentally in somatic cells by heat shock . Thus heat shock may be a condition that ordinarily triggers sex-inducing pheromone in nature. The Closterium peracerosum-strigosum-littorale (C. psl) complex
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#17328511670913224-407: The next generation via asexual reproduction of the host, but because the endosymbionts are larger than the foraminiferal gametes , they need to acquire algae horizontally following sexual reproduction. Several species of radiolaria have photosynthetic symbionts. In some species the host digests algae to keep the population at a constant level. Hatena arenicola is a flagellate protist with
3286-422: The ocean like that of the North Atlantic. In such waters, cell growth of larger phytoplankton such as diatoms is limited by (insufficient) nitrate concentrations. Endosymbiotic bacteria fix nitrogen for their hosts and in turn receive organic carbon from photosynthesis. These symbioses play an important role in global carbon cycling . One known symbiosis between the diatom Hemialus spp. and
3348-417: The order Charales do exist, but are rare. The fossil record of the Charales consists mostly of gyrogonites , that is, calcified fructifications or, more exactly, calcified spiral cells surrounding the oospores. It may be noted that the gyrogonites are studied by palaeontologists , but not often destroyed (using acids) during neontological research to liberate the oospores. The oldest known representative of
3410-722: The origins of symbioses in general, as a proxy for understanding endosymbiosis in other species. The best-studied ant endosymbionts are Blochmannia bacteria, which are the primary endosymbiont of Camponotus ants. In 2018 a new ant-associated symbiont, Candidatus Westeberhardia Cardiocondylae, was discovered in Cardiocondyla . It is reported to be a primary symbiont. The pea aphid ( Acyrthosiphon pisum ) contains at least three secondary endosymbionts, Hamiltonella defensa , Regiella insecticola , and Serratia symbiotica . Hamiltonella defensa defends its aphid host from parasitoid wasps. This symbiosis replaces lost elements of
3472-413: The production of a cell plate . Photosynthetic eukaryotes originated following a primary endosymbiotic event, where a heterotrophic eukaryotic cell engulfed a photosynthetic cyanobacterium -like prokaryote that became stably integrated and eventually evolved into a membrane-bound organelle : the plastid . This primary endosymbiosis event gave rise to three autotrophic clades with primary plastids:
3534-541: The propensity for novel functions as seen in the plant-bacterium interaction ( holobiont formation). Vertical transmission takes place when the symbiont moves directly from parent to offspring. In horizontal transmission each generation acquires symbionts from the environment. An example is nitrogen-fixing bacteria in certain plant roots, such as pea aphid symbionts. A third type is mixed-mode transmission, where symbionts move horizontally for some generations, after which they are acquired vertically. Wigglesworthia ,
3596-403: The putative primary role of Buchnera is to synthesize essential amino acids that the aphid cannot acquire from its diet of plant sap. The primary role of Wigglesworthia is to synthesize vitamins that the tsetse fly does not get from the blood that it eats. In lower termites, the endosymbiotic protists play a major role in the digestion of lignocellulosic materials that constitute a bulk of
3658-405: The symbiosis is obligate. Nutritionally-enhanced diets allow symbiont-free specimens to survive, but they are unhealthy, and at best survive only a few generations. In some insect groups, these endosymbionts live in specialized insect cells called bacteriocytes (also called mycetocytes ), and are maternally-transmitted, i.e. the mother transmits her endosymbionts to her offspring. In some cases,
3720-428: The termites' diet. Bacteria benefit from the reduced exposure to predators and competition from other bacterial species, the ample supply of nutrients and relative environmental stability inside the host. Primary endosymbionts of insects have among the smallest of known bacterial genomes and have lost many genes commonly found in closely related bacteria. One theory claimed that some of these genes are not needed in
3782-440: The three paths for symbiont transfer. Horizontal symbiont transfer ( horizontal transmission ) is a process where a host acquires a facultative symbiont from the environment or another host. The Rhizobia-Legume symbiosis (bacteria-plant endosymbiosis) is a prime example of this modality. The Rhizobia-legume symbiotic relationship is important for processes such as the formation of root nodules. It starts with flavonoids released by
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#17328511670913844-963: Was a unicellular flagellate. The Viridiplantae diverged into two clades. The Chlorophyta include the early diverging prasinophyte lineages and the core Chlorophyta, which contain the majority of described species of green algae. The Streptophyta include charophytes and land plants. Below is a consensus reconstruction of green algal relationships, mainly based on molecular data. Palmophyllophyceae (prasinophyte clade VI) Prasinodermophyceae Ulvophyceae Chlorophyceae Trebouxiophyceae Chlorodendrophyceae Pedinophyceae Prasinophytes Clade VIIA Prasinophytes Clade VIIC Pycnococcaceae Nephroselmidophyceae Mamiellophyceae Pyramimonadales Mesostigmatophyceae Spirotaenia Chlorokybophyceae Streptofilum Klebsormidiophyceae Charophyceae Coleochaetophyceae Zygnematophyceae Mesotaeniaceae s.s. Embryophyta (land plants) The basal character of
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