Mycoheterotrophy
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Myco-heterotrophy (from
Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
, , and ) is a
symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...
relationship between certain kinds of
plants Plants are the eukaryotes that form the kingdom Plantae; they are predominantly photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with cyanobacteria to produce sugars f ...
and
fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
, in which the plant gets all or part of its food from
parasitism Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...
upon fungi rather than from
photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...
. A myco-heterotroph is the
parasitic plant A parasitic plant is a plant that derives some or all of its nutritional requirements from another living plant. They make up about 1% of angiosperms and are found in almost every biome. All Parasite, parasitic plants develop a specialized organ ...
partner in this relationship. Myco-heterotrophy is considered a kind of
cheating Cheating generally describes various actions designed to subvert or disobey rules in order to obtain unfair advantages without being noticed. This includes acts of bribery, cronyism and nepotism in any situation where individuals are given pr ...
relationship and myco-heterotrophs are sometimes informally referred to as "mycorrhizal cheaters". This relationship is sometimes referred to as mycotrophy, though this term is also used for plants that engage in mutualistic
mycorrhizal A mycorrhiza (; , mycorrhiza, or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant's rhizosphere, the plant root system and its surroundings. Mycorrhizae play ...
relationships.


Relationship between myco-heterotrophs and host fungi

Full (or obligate) myco-heterotrophy exists when a non-photosynthetic plant (a plant largely lacking in
chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...
or otherwise lacking a functional
photosystem Photosystems are functional and structural units of protein complexes involved in photosynthesis. Together they carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons. Photosystems ...
) gets all of its food from the fungi that it parasitizes. Partial (or facultative) myco-heterotrophy exists when a plant is capable of photosynthesis, but parasitizes fungi as a supplementary food supply. There are also plants, such as some
orchid Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Orchids are cosmopolitan plants that are found in almost every habitat on Eart ...
species (e.g., ''
Neottia nidus-avis ''Neottia nidus-avis'', the bird's-nest orchid, is a non-photosynthetic orchid, native to Europe, Russia, with sporadic presence in North-Africa, and some parts of the Middle East. Description ''Neottia nidus-avis'' grows to tall and each sh ...
''), that are non-photosynthetic and obligately myco-heterotrophic for part of their
life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from conception to reproduction *Life-cycle hypothesis, in economics *Erikson's stages of psy ...
, and photosynthetic and facultatively myco-heterotrophic or non-myco-heterotrophic for the rest of their life cycle. Not all non-photosynthetic or "
achlorophyllous Myco-heterotrophy (from Greek , , and ) is a symbiotic relationship between certain kinds of plants and fungi, in which the plant gets all or part of its food from parasitism upon fungi rather than from photosynthesis. A myco-heterotroph i ...
" plants are myco-heterotrophic – some non-photosynthetic plants like
dodder ''Cuscuta'' (), commonly known as dodder or amarbel, is a genus of over 201 species of yellow, orange, or red (rarely green) parasitic plants. Formerly treated as the only genus in the family Cuscutaceae, it now is accepted as belonging in the ...
directly parasitize the
vascular tissue Vascular tissue is a complex transporting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. T ...
of other plants. The partial or full loss of photosynthesis is reflected by extreme physical and functional reductions of plastid genomes in mycoheterophic plants, an ongoing evolutionary process. In the past, non-photosynthetic plants were mistakenly thought to get food by breaking down
organic matter Organic matter, organic material or natural organic matter is the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come fro ...
in a manner similar to
saprotrophic Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ...
fungi. Such plants were therefore called " saprophytes". It is now known that these plants are not physiologically capable of directly breaking down organic matter and that in order to get food, non-photosynthetic plants must engage in parasitism, either through myco-heterotrophy or direct parasitism of other plants. The interface between the plant and fungal partners in this association is between the roots of the plant and the mycelium of the fungus. Myco-heterotrophy therefore closely resembles
mycorrhiza A mycorrhiza (; , mycorrhiza, or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant's rhizosphere, the plant root system and its surroundings. Mycorrhizae play ...
(and indeed is thought to have evolved from mycorrhiza), except that in myco-heterotrophy, the flow of carbon is from the fungus to the plant, rather than vice versa. Most myco-heterotrophs can therefore be seen as ultimately being
epiparasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...
, since they take energy from fungi that in turn get their energy from
vascular plants Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified tissue ( ...
. Indeed, much myco-heterotrophy takes place in the context of common
mycorrhizal network A mycorrhizal network (also known as a common mycorrhizal network or CMN) is an underground network found in forests and other plant communities, created by the hyphae of mycorrhizal fungi joining with plant roots. This network connects individ ...
s, in which plants use mycorrhizal fungi to exchange carbon and nutrients with other plants. In these systems, myco-heterotrophs play the role of "mycorrhizal cheaters", taking carbon from the common network, with no known reward. A special form of mycoheterotrophic association, which appears to be a chimera between the haustorial parasitism of a
parasitic plant A parasitic plant is a plant that derives some or all of its nutritional requirements from another living plant. They make up about 1% of angiosperms and are found in almost every biome. All Parasite, parasitic plants develop a specialized organ ...
and mycoheterotrophy, is observed in ''
Parasitaxus usta ''Parasitaxus usta'', also known in French as ''cèdre rabougri'', is a rare species of conifer of the family Podocarpaceae, and the sole species of the genus ''Parasitaxus''. Description It is a woody shrub up to 1.8 m endemic to the remote ...
'', the only mycoheterotrophic
gymnosperm The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...
. In congruence with older reports, it has been recently shown that some myco-heterotrophic orchids can be supported by saprotrophic fungi, exploiting litter- or wood-decaying fungi. In addition, several green plants (evolutionarily close to myco-heterotrophic species) have been shown to engage in partial myco-heterotrophy, that is, they are able to take carbon from mycorrhizal fungi, in addition to their photosynthetic intake.


Species diversity of myco-heterotrophs and host fungi

Myco-heterotrophs are found among several plant groups, mainly
flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
s. All
monotropes Monotropoideae, sometimes referred to as monotropes, are a flowering plant subfamily in the family Ericaceae. Members of this subfamily are notable for their mycoheterotrophic and non-photosynthesizing or achlorophyllous characteristics. Descript ...
and non-photosynthetic
orchids Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Orchids are cosmopolitan plants that are found in almost every habitat on Earth ...
are full myco-heterotrophs, as is the non-photosynthetic
liverwort Liverworts are a group of non-vascular land plants forming the division Marchantiophyta (). They may also be referred to as hepatics. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry ...
''
Aneura mirabilis ''Aneura'' may refer to: * ''Aneura'' (fly), a genus of insects in the family Mycetophilidae * ''Aneura'' (plant), a genus of liverworts in the family Aneuraceae {{genus disambiguation ...
'' (previously considered a species of ''Cryptothallus''). Partial myco-heterotrophy is common in the
Gentian family Gentianaceae is a family of flowering plants of 105 genera and about 1600 species. Etymology The family takes its name from the genus ''Gentiana'', named after the Illyrian king Gentius. Distribution Distribution is cosmopolitan. Characteristi ...
, with a few genera such as ''
Voyria ''Voyria'', commonly known as ghostplants, is a genus of 20 species of herbaceous perennial plants, belonging to the family Gentianaceae. They are mostly native to warm temperate and tropical regions of the Caribbean, Central America and South A ...
'' being fully myco-heterotrophic; in photosynthetic orchids; and in a number of other plant groups. Some
fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...
s and
clubmosses Lycopodiopsida is a class of vascular plants also known as lycopsids, lycopods, or lycophytes. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching stems bearing simple leaves ...
have myco-heterotrophic
gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the se ...
stages.Taylor DL, Bruns TD, Leake JR, Read DJ. 2002
Mycorrhizal specificity and function in myco-heterotrophic plants.
In: ''Mycorrhizal Ecology'' (Sanders IR, van der Heijden M, eds.), Ecological Studies vol. 157, pp 375–414. Berlin: Springer-Verlag. . (NOTE: this PDF is from the page proofs, and is not identical to the published version)
The fungi that are parasitized by myco-heterotrophs are typically fungi with large energy reserves to draw on, usually mycorrhizal fungi, though there is some evidence that they may also parasitize parasitic fungi that form extensive mycelial networks, such as ''
Armillaria ''Armillaria'' is a genus of fungi that includes the '' A. mellea'' species ('honey fungus') that live on trees and woody shrubs. It includes about 10 species formerly categorized summarily as ''A. mellea''. ''Armillaria'' sp. are long-live ...
''. Examples of fungi parasitized by myco-heterotrophic plants can be found among the
ectomycorrhizal An ectomycorrhiza (from Greek ἐκτός ', "outside", μύκης ', "fungus", and ῥίζα ', "root"; ectomycorrhizas or ectomycorrhizae, abbreviated EcM) is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobion ...
, arbuscular mycorrhizal, and orchid mycorrhizal fungi. The great diversity in unrelated plant families with myco-heterotrophic members, as well as the diversity of fungi targeted by myco-heterotrophs, suggests multiple
parallel evolution Parallel evolution is the similar development of a trait in distinct species that are not closely related, but share a similar original trait in response to similar evolutionary pressure.Zhang, J. and Kumar, S. 1997Detection of convergent and pa ...
s of myco-heterotrophs from mycorrhizal ancestors.


References


Further reading

* * * Werner PG. 2006
Myco-heterotrophs: hacking the mycorrhizal network.
''
Mycena News ''Mycena'' is a genus of about 500 species of fungi. Rarely more than a few centimeters in width, the mushrooms are characterized by a small conical or bell-shaped cap and a thin fragile stem. Most are grey or brown, but a few species have brigh ...
'' 57(3): 1,8.
Dr. Martin Bidartondo: Selected publications





External links



''The Parasitic Plant Connection'', SIU Carbondale, College of Science.
''Wayne's Word'' Noteworthy Plant For June 1997: Fungus Flowers – Flowering Plants that Resemble Fungi
by WP Armstrong.

by Tom Volk, ''TomVolkFungi.net''

– images of myco-heterotrophs by mycologist Martín Bidartondo. {{DEFAULTSORT:Myco-Heterotrophy Botany Ecology Mycology * Parasites of fungi Symbiosis