Neotyphodium
Encyclopedia
Neotyphodium is a form genus
containing species of endophytic fungi. These endophytes are asexual
, seed-borne symbionts of cool-season grass
es, and grow intercellularly throughout the aerial tissues of their host
s, including shoot apical meristem
s, leaf sheaths and blades, inflorescences, seeds and embryos. The Neotyphodium endophytes produce at least four different classes of compounds with various biological activities (toxicity
or feeding deterrence) against insect and mammalian herbivores.
) are closely related to teleomorphic species of the genus Epichloë
, from which many have evolved by processes involving interspecific hybridization. Molecular phylogenetic evidence demonstrates that asexual Neotyphodium species are derived either from individual Epichloë species, or more commonly, from hybrids with at least two ancestral Epichloë species. Hence, the form genus Neotyphodium is very closely associated with the teleomorphic genus Epichloë. In keeping with the code of botanical nomenclature, the form genus refers to the asexual spore or vegetative state, and the teleomorphic genus refers to the sexual state. Because of their close relationships and shared biological properties, members of these two genera are collectively called 'epichloae' (singular = 'epichloë').
occurs by vertical transmission, i.e., fungal growth into newly developing host tillers (=individual grass plants). Importantly, all Neotyphodium and some Epichloë
species infect new grass plants solely by growing into the seeds of their grass hosts, and infecting the growing seedling. Manifestation of the sexual state — which only occurs in Epichloë species — causes choke disease, a condition in which grass inflorescence
s are engulfed by rapid fungal outgrowth forming a stroma. The fungal stroma suppresses host seed production and culminates in the ejection of meiospores (ascospore
s) that mediate horizontal (contagious) transmission of the fungus to new plants. So, the two transmission modes exclude each other, although in many grass-Epichloë symbiota the fungus actually displays both transmission modes simultaneously, by choking some tillers and transmitting in seeds produced by unchoked tillers.
While being obligate
symbionts in nature, most epichloae are readily culturable in the laboratory
on culture media such as potato dextrose agar
or a minimal salts broth supplemented with thiamine, sugars or sugar alcohols, and organic nitrogen or ammonium.
that has spawned today's pooid
grasses. This is suggested by phylogenetic studies indicating preponderance of codivergence of Neotyphodium/Epichloë species with the grass hosts they inhabit. Growth of the fungal symbiont is very tightly regulated within its grass host, indicated by a largely unbranched mycelial
morphology and remarkable synchrony of grass leaf and hypha
l extension of the fungus; the latter seems to occur via a mechanism that involves stretch-induced or intercalary elongation of the endophyte's hyphae, a process so far not found in any other fungal species, indicating specialized adaptation of the fungus to the dynamic growth environment inside its host. A complex NADPH oxidase
enzyme-based ROS
-generating system in epichloae is indispensable for maintenance of this growth synchrony. Thus, it has been demonstrated that deletion of genes encoding these enzymes in Epichloë festucae causes severely disordered fungal growth in grass tissues and even death of the grass plant.
is intimately tied to that of their hosts. In fact, some positive effects of epichloae on their host plants include increased growth, drought tolerance, and herbivore
and pathogen
resistance. Resistance against herbivores has been attributed to alkaloid
s produced by the symbiotic epichloae. Although grass-epichloë symbioses have been widely recognized to be mutualistic in many wild and cultivated grasses, the interactions can be highly variable and sometimes antagonistic, especially under nutrient-poor conditions in the soil.
Due to the relatively large number of grass species harboring epichloae and the variety of environments in which they occur, the mechanisms underlying beneficial or antagonistic outcomes of epichloë-grass symbioses are difficult to delineate in natural and also agricultural environments. Some studies suggest a relationship between grazing by herbivores and increased epichloë infestation of the grasses on which they feed, whereas others indicate a complex interplay between plant species and fungal symbionts in response to herbivory or environmental conditions. The strong anti-herbivore activities of several bioactive compounds produced by the epichloae and relatively modest direct effects of the epichloae on plant growth and physiology suggest that these compounds play a major role in the persistence of the symbiosis.
compounds with biological activities against a broad range of herbivores. Ergoline
alkaloids (which are ergot alkaloids, named after the ergot
fungus, Claviceps purpurea, a close relative of the epichloae) are characterized by a ring system derived from 4-prenyl tryptophan
. Among the most abundant ergot alkaloids in epichloë-symbiotic grasses is ergovaline, comprising an ergoline moiety attached to a bicyclic tripeptide
containing the amino acids L-proline
, L-alanine
, and L-valine
. Key genes and enzymes for ergot alkaloid biosynthesis have been identified in epichloae and include dmaW, encoding dimethylallyl-tryptophan synthase
and lpsA, a non-ribosomal peptide synthetase
.
Another group of epichloë alkaloids are the indole
-diterpenoids, such as lolitrem B, which are produced from the activity of several enzymes, including prenyltransferase
s and various monooxygenase
s. Both the ergoline and indole-diterpenoid alkaloids have biological activity
against mammalian herbivores, and also activity against some insects. Peramine is a pyrrolopyrazine alkaloid thought to be biosynthesized from the guanidinium
-group-containing amino acid L-arginine
, and pyrrolidine-5-carboxylate, a precursor of L-proline
, and is an insect-feeding deterrent. The loline alkaloids
are 1-aminopyrrolizidines with an oxygen atom linking bridgehead carbons 2 and 7, and are biosynthesized from the amino acids L-proline and L-homoserine
. The lolines have insecticidal
and insect-deterrent activities comparable to nicotine
. Loline accumulation is strongly induced in young growing tissues or by damage to the plant-fungus symbiotum. Many, but not all, epichloae produce up to three classes of these alkaloids in various combinations and amounts.
Form taxon
Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships...
containing species of endophytic fungi. These endophytes are asexual
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
, seed-borne symbionts of cool-season grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...
es, and grow intercellularly throughout the aerial tissues of their host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
s, including shoot apical meristem
Meristem
A meristem is the tissue in most plants consisting of undifferentiated cells , found in zones of the plant where growth can take place....
s, leaf sheaths and blades, inflorescences, seeds and embryos. The Neotyphodium endophytes produce at least four different classes of compounds with various biological activities (toxicity
Toxicity
Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...
or feeding deterrence) against insect and mammalian herbivores.
Taxonomic considerations
Neotyphodium species (with the likely exception of N. chilenseNeotyphodium chilense
Neotyphodium chilense is a species of fungus in the Clavicipitaceae family. Originally known as Acremonium chilense when it was first described in 1990, it was transferred to Neotyphodium in 1996. It is an endophytic fungus that occurs in Dactylis glomerata in southern Chile....
) are closely related to teleomorphic species of the genus Epichloë
Epichloë
Epichloë species and their close relatives, the Neotyphodium species, are systemic and constitutive symbionts of cool-season grasses , and belong to the fungal family Clavicipitaceae...
, from which many have evolved by processes involving interspecific hybridization. Molecular phylogenetic evidence demonstrates that asexual Neotyphodium species are derived either from individual Epichloë species, or more commonly, from hybrids with at least two ancestral Epichloë species. Hence, the form genus Neotyphodium is very closely associated with the teleomorphic genus Epichloë. In keeping with the code of botanical nomenclature, the form genus refers to the asexual spore or vegetative state, and the teleomorphic genus refers to the sexual state. Because of their close relationships and shared biological properties, members of these two genera are collectively called 'epichloae' (singular = 'epichloë').
Life cycle
The taxonomic dichotomy is especially interesting in this group of symbionts, because vegetative propagation of fungal myceliumMycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
occurs by vertical transmission, i.e., fungal growth into newly developing host tillers (=individual grass plants). Importantly, all Neotyphodium and some Epichloë
Epichloë
Epichloë species and their close relatives, the Neotyphodium species, are systemic and constitutive symbionts of cool-season grasses , and belong to the fungal family Clavicipitaceae...
species infect new grass plants solely by growing into the seeds of their grass hosts, and infecting the growing seedling. Manifestation of the sexual state — which only occurs in Epichloë species — causes choke disease, a condition in which grass inflorescence
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
s are engulfed by rapid fungal outgrowth forming a stroma. The fungal stroma suppresses host seed production and culminates in the ejection of meiospores (ascospore
Ascospore
An ascospore is a spore contained in an ascus or that was produced inside an ascus. This kind of spore is specific to fungi classified as ascomycetes ....
s) that mediate horizontal (contagious) transmission of the fungus to new plants. So, the two transmission modes exclude each other, although in many grass-Epichloë symbiota the fungus actually displays both transmission modes simultaneously, by choking some tillers and transmitting in seeds produced by unchoked tillers.
While being obligate
Obligate
Obligate means "by necessity" and is used mainly in biology in phrases such as:* Obligate aerobe, an organism that cannot survive without oxygen* Obligate anaerobe, an organism that cannot survive in the presence of oxygen...
symbionts in nature, most epichloae are readily culturable in the laboratory
Laboratory
A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...
on culture media such as potato dextrose agar
Potato dextrose agar
Potato dextrose agar and potato dextrose broth are common microbiological growth media made from potato infusion, and dextrose...
or a minimal salts broth supplemented with thiamine, sugars or sugar alcohols, and organic nitrogen or ammonium.
Coevolution and growth synchrony with grass hosts
The epichloae display a number of central features that suggest a very strong and ancient association with their grass hosts. The symbiosis appears to have existed already during the early grass evolutionEvolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
that has spawned today's pooid
Pooideae
The Pooideae is a subfamily of the true grass family Poaceae. It includes some major cereals such as wheat, barley, oat, rye and many lawn and pasture grasses.- List :...
grasses. This is suggested by phylogenetic studies indicating preponderance of codivergence of Neotyphodium/Epichloë species with the grass hosts they inhabit. Growth of the fungal symbiont is very tightly regulated within its grass host, indicated by a largely unbranched mycelial
Mycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
morphology and remarkable synchrony of grass leaf and hypha
Hypha
A hypha is a long, branching filamentous structure of a fungus, and also of unrelated Actinobacteria. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium; yeasts are unicellular fungi that do not grow as hyphae.-Structure:A hypha consists of one or...
l extension of the fungus; the latter seems to occur via a mechanism that involves stretch-induced or intercalary elongation of the endophyte's hyphae, a process so far not found in any other fungal species, indicating specialized adaptation of the fungus to the dynamic growth environment inside its host. A complex NADPH oxidase
NADPH oxidase
The NADPH oxidase is a membrane-bound enzyme complex. It can be found in the plasma membrane as well as in the membrane of phagosome.-Subunits:It is made up of six subunits...
enzyme-based ROS
Reactive oxygen species
Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....
-generating system in epichloae is indispensable for maintenance of this growth synchrony. Thus, it has been demonstrated that deletion of genes encoding these enzymes in Epichloë festucae causes severely disordered fungal growth in grass tissues and even death of the grass plant.
Effects on the grass plant and on herbivores
It has been proposed that vertically transmitted symbionts should evolve to be mutualists since their reproductive fitnessFitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
is intimately tied to that of their hosts. In fact, some positive effects of epichloae on their host plants include increased growth, drought tolerance, and herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
and pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
resistance. Resistance against herbivores has been attributed to alkaloid
Alkaloid
Alkaloids are a group of naturally occurring chemical compounds that contain mostly basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Also some synthetic compounds of similar structure are attributed to alkaloids...
s produced by the symbiotic epichloae. Although grass-epichloë symbioses have been widely recognized to be mutualistic in many wild and cultivated grasses, the interactions can be highly variable and sometimes antagonistic, especially under nutrient-poor conditions in the soil.
Due to the relatively large number of grass species harboring epichloae and the variety of environments in which they occur, the mechanisms underlying beneficial or antagonistic outcomes of epichloë-grass symbioses are difficult to delineate in natural and also agricultural environments. Some studies suggest a relationship between grazing by herbivores and increased epichloë infestation of the grasses on which they feed, whereas others indicate a complex interplay between plant species and fungal symbionts in response to herbivory or environmental conditions. The strong anti-herbivore activities of several bioactive compounds produced by the epichloae and relatively modest direct effects of the epichloae on plant growth and physiology suggest that these compounds play a major role in the persistence of the symbiosis.
Bioactive compounds
Many Neotyphodium endophytes produce a diverse range of natural productNatural product
A natural product is a chemical compound or substance produced by a living organism - found in nature that usually has a pharmacological or biological activity for use in pharmaceutical drug discovery and drug design...
compounds with biological activities against a broad range of herbivores. Ergoline
Ergoline
Ergoline is a chemical compound whose structural skeleton is contained in a diverse range of alkaloids including a few psychedelic drugs . Ergoline derivatives are used clinically for the purpose of vasoconstriction and in the treatment of migraines and Parkinson's disease...
alkaloids (which are ergot alkaloids, named after the ergot
Ergot
Ergot or ergot fungi refers to a group of fungi of the genus Claviceps. The most prominent member of this group is Claviceps purpurea. This fungus grows on rye and related plants, and produces alkaloids that can cause ergotism in humans and other mammals who consume grains contaminated with its...
fungus, Claviceps purpurea, a close relative of the epichloae) are characterized by a ring system derived from 4-prenyl tryptophan
Tryptophan
Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...
. Among the most abundant ergot alkaloids in epichloë-symbiotic grasses is ergovaline, comprising an ergoline moiety attached to a bicyclic tripeptide
Tripeptide
A tripeptide is a peptide consisting of three amino acids joined by peptide bonds.Examples of tripeptides are:*Eisenin is a peptide with immunological activity that is isolated from the Japanese marine alga, Eisenia bicyclis, which more commonly is known as, Arame*GHK-Cu is a human copper binding...
containing the amino acids L-proline
Proline
Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that the human body can synthesize it. It is unique among the 20 protein-forming amino acids in that the α-amino group is secondary...
, L-alanine
Alanine
Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 amino acids encoded by the genetic code. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...
, and L-valine
Valine
Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...
. Key genes and enzymes for ergot alkaloid biosynthesis have been identified in epichloae and include dmaW, encoding dimethylallyl-tryptophan synthase
Tryptophan dimethylallyltransferase
In enzymology, a tryptophan dimethylallyltransferase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are dimethylallyl diphosphate and L-tryptophan, whereas its two products are diphosphate and 4--L-tryptophan.This enzyme belongs to the family of...
and lpsA, a non-ribosomal peptide synthetase
Nonribosomal peptide
Nonribosomal peptides are a class of peptide secondary metabolites, usually produced by microorganisms like bacteria and fungi. Nonribosomal peptides are also found in higher organisms, such as nudibranchs, but are thought to be made by bacteria inside these organisms...
.
Indole
Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. Indole is a popular component of fragrances and the precursor to many pharmaceuticals. Compounds that contain an...
-diterpenoids, such as lolitrem B, which are produced from the activity of several enzymes, including prenyltransferase
Prenyltransferase
Prenyltransferases are a class of enzymes that transfer allylic prenyl groups to acceptor molecules. Prenyl transferases commonly refer to prenyl diphosphate synthases....
s and various monooxygenase
Monooxygenase
Monooxygenases are enzymes that incorporate one hydroxyl group into substrates in many metabolic pathways. In this reaction, two atoms of dioxygen are reduced to one hydroxyl group and one H2O molecule by the concomitant oxidation of NADH.-Classification:...
s. Both the ergoline and indole-diterpenoid alkaloids have biological activity
Biological activity
In pharmacology, biological activity or pharmacological activity describes the beneficial or adverse effects of a drug on living matter. When a drug is a complex chemical mixture, this activity is exerted by the substance's active ingredient or pharmacophore but can be modified by the other...
against mammalian herbivores, and also activity against some insects. Peramine is a pyrrolopyrazine alkaloid thought to be biosynthesized from the guanidinium
Guanidine
Guanidine is a crystalline compound of strong alkalinity formed by the oxidation of guanine. It is used in the manufacture of plastics and explosives. It is found in urine as a normal product of protein metabolism. The molecule was first synthesized in 1861 by the oxidative degradation of an...
-group-containing amino acid L-arginine
Arginine
Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. At the level of molecular genetics, in the structure of the messenger ribonucleic acid mRNA, CGU, CGC, CGA, CGG, AGA, and AGG, are the triplets of nucleotide bases or codons that codify for arginine during...
, and pyrrolidine-5-carboxylate, a precursor of L-proline
Proline
Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that the human body can synthesize it. It is unique among the 20 protein-forming amino acids in that the α-amino group is secondary...
, and is an insect-feeding deterrent. The loline alkaloids
Loline alkaloids
A loline alkaloid is a member of the 1-aminopyrrolizidines , which are bioactive natural products with several distinct biological and chemical features...
are 1-aminopyrrolizidines with an oxygen atom linking bridgehead carbons 2 and 7, and are biosynthesized from the amino acids L-proline and L-homoserine
Homoserine
Homoserine is an α-amino acid with the chemical formula HO2CCHCH2CH2OH. L-Homoserine is not one of the common amino acids encoded by DNA. It differs from the proteinogenic amino acid serine by insertion of an additional methylene group...
. The lolines have insecticidal
Insecticidal
Insecticidal is a 2005 [Horror Thriller featuring giant, killer insects. A college student is modifying insects until a housemate tries to kill them...
and insect-deterrent activities comparable to nicotine
Nicotine
Nicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
. Loline accumulation is strongly induced in young growing tissues or by damage to the plant-fungus symbiotum. Many, but not all, epichloae produce up to three classes of these alkaloids in various combinations and amounts.
Species
- Neotyphodium aotearoaeNeotyphodium aotearoaeNeotyphodium aotearoae is a systemic and seed-transmissible symbiont of Echinopogon ovatus, a grass endemic to Australia and New Zealand. The fungus produces the anti-insect loline alkaloids. Unlike most Neotyphodium species, N. aotearoae does not appear to be a hybrid. Its closest...
- Neotyphodium australienseNeotyphodium australienseNeotyphodium australiense is a systemic and seed-transmissible symbiont of Echinopogon ovatus, a grass endemic to Australia and New Zealand / Aotearoa. To date, N. australiense has only been found in some Australian populations of this grass, whereas other populations in Australia and New...
- Neotyphodium chilenseNeotyphodium chilenseNeotyphodium chilense is a species of fungus in the Clavicipitaceae family. Originally known as Acremonium chilense when it was first described in 1990, it was transferred to Neotyphodium in 1996. It is an endophytic fungus that occurs in Dactylis glomerata in southern Chile....
- Neotyphodium chisosum
- Neotyphodium coenophialumNeotyphodium coenophialumNeotyphodium coenophialum is a systemic and seed-transmissible symbiont of Schedonorus arundinaceus , a grass endemic to Eurasia and North Africa, but widely naturalized in North America, Australia and New Zealand / Aotearoa...
- Neotyphodium gansuense
- Neotyphodium huerfanum
- Neotyphodium lolii
- Neotyphodium melicicolaNeotyphodium melicicolaNeotyphodium melicicola is a systemic and seed-transmissible symbiont of Melica decumbens and Melica racemosa, grasses endemic to southern Africa.. These species are called 'dronkgras' because they can cause staggers in grazing livestock...
- Neotyphodium occultans
- Neotyphodium siegelii
- Neotyphodium starrii
- Neotyphodium tembladerae
- Neotyphodium typhinum
- Neotyphodium uncinatum
- Neotyphodium sinicum
- Neotyphodium sinofestucae