Plant use of endophytic fungi in defense

Plant use of endophytic fungi in defense occurs when endophytic

Endophyte

An endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life without causing apparent disease. Endophytes are ubiquitous and have been found in all the species of plants studied to date; however, most of these endophyte/plant relationships...

fungi

Fungus

A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

, which live symbiotically

Symbiosis

Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...

with the majority of plants by entering their cells, are utilized as an indirect defense against herbivores. In exchange for carbohydrate energy resources, the fungus provides benefits to the plant which can include increased water or nutrient uptake and protection from phytophagous insects, birds or mammals. Once associated, the fungi alter nutrient content of the plant and enhance or begin production of secondary metabolites. The change in chemical composition acts to deter herbivory by insects, grazing by ungulates

Ungulate

Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...

and/or oviposition

Oviposition

Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....

by adult insects. Endophyte-mediated defense can also be effective against pathogens and non-herbivory damage.

This differs from other forms of indirect defense in that the fungi live within the plant cells and directly alter their physiology. In contrast, other biotic defenses such as predators or parasites of the herbivores consuming a plant are normally attracted by volatile organic compounds (known as semiochemicals) released following damage or by food rewards and shelter produced by the plant. These defenders vary in the time spent with the plant: from long enough to oviposit to remaining there for numerous generations, as in the ant-acacia mutualism. Endophytic fungi tend to live with the plant over its entire life.

Diversity of endophytic associations

The fungal endophytes are a diverse group of organisms forming associations almost ubiquitously throughout the plant kingdom

Kingdom (biology)

In biology, kingdom is a taxonomic rank, which is either the highest rank or in the more recent three-domain system, the rank below domain. Kingdoms are divided into smaller groups called phyla or divisions in botany...

. The endophytes which provide indirect defense against herbivores may have come from a number of origins, including mutualistic root endophyte associations and the evolution of entomopathogenic fungi

Entomopathogenic fungus

An entomopathogenic fungus is a fungus that can act as a parasite of insects and kills or seriously disables them.-Typical life cycle:These fungi usually attach to the external body surface of insects in the form of microscopic spores...

into plant-associated endophytes. The endomycorrhiza, which live in plant roots, are made up of five groups: arbuscular

Arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi are all placed in the phylum Glomeromycota. They form the widespread arbuscular mycorrhiza symbiosis with land plants . The fungi are obligate symbionts that cannot be cultured without a plant as a 'host'...

, arbutoid, ericoid, monotropoid, and orchid mycorrhizae. The majority of species are from the phylum

Phylum

In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

Glomeromycota

Glomeromycota is one of seven currently recognized phyla within the kingdom Fungi, with approximately 230 described species. Members of the Glomeromycota form arbuscular mycorrhizas with the roots or thalli of land plants. Geosiphon pyriformis forms an endocytobiotic association with Nostoc...

with the ericoid species coming from the Ascomycota

Ascomycota

The Ascomycota are a Division/Phylum of the kingdom Fungi, and subkingdom Dikarya. Its members are commonly known as the Sac fungi. They are the largest phylum of Fungi, with over 64,000 species...

, while the arbutoid, monotropoid and orchid mycorrhizae are classified as Basidiomycota

Basidiomycota

Basidiomycota is one of two large phyla that, together with the Ascomycota, comprise the subkingdom Dikarya within the Kingdom Fungi...

. The entomopathogenic view has gained support from observations of increased fungal growth in response to induced plant defenses and colonization of plant tissues.

Examples of host specialists

Generalist and specialist species

A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources . A specialist species can only thrive in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either...

are numerous – especially in temperate environments – with multiple specialist fungi frequently infecting one plant individual simultaneously. These specialists demonstrate high levels of specificity for their host species and may form physiologically adapted

Adaptation

An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....

host-races on closely related congeners. Piriformospora indica is an interesting endophytic fungus of the order Sebacinales

Sebacinales

The Sebacinales are an order of fungi in the class Agaricomycetes. Taxa have a widespread distribution and are mostly terrestrial, many forming mycorrhizas with a wide variety of plants, including orchids. The order is monotypic, containing a single family, the Sebacinaceae. There are 8 genera and...

, the fungus is capable of colonising roots and forming symbiotic relationship with every possible plant on earth . P. indica has also been shown to increase both crop yield and plant defence of a variety of crops(barley, tomato, maize etc.) against root-pathogens. However, there are also many examples of generalist

Generalist and specialist species

fungi which may occur on different hosts at different frequencies (e.g. Acremonium endophytes from five subgenera of Festuca) and as part of a variety of fungal assemblages. They may even spread to novel, introduced plant species

Introduced species

An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...

. Endophytic mutualists associate with species representative of every growth form and life history

Life history theory

Life history theory posits that the schedule and duration of key events in an organism's lifetime are shaped by natural selection to produce the largest possible number of surviving offspring...

strategy in the grasses and many other groups of plants. The effects of associating with multiple strains

Strain (biology)

In biology, a strain is a low-level taxonomic rank used in three related ways.-Microbiology and virology:A strain is a genetic variant or subtype of a micro-organism . For example, a "flu strain" is a certain biological form of the influenza or "flu" virus...

or species of fungus at once can vary, but in general, one type of fungus will be providing the majority of benefit to the plant.

Secondary metabolite production

Some chemical defenses once thought to be produced by the plant have since been shown to be synthesized by endophytic fungi. The chemical basis of insect resistance in endophyte-plant defense mutualisms has been most extensively studied in the perennial ryegrass

Ryegrass

Ryegrass is a genus of nine species of tufted grasses in the Pooideae subfamily of the Poaceae family. Also called tares , these plants are native to Europe, Asia and northern Africa, but are...

and three major classes of secondary metabolites are found: indole diterpenes, ergot alkaloids and peramine. Related compounds are found across the range of endophytic fungal associations with plants. The terpenes

Terpene

Terpenes are a large and diverse class of organic compounds, produced by a variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium. They are often strong smelling and thus may have had a protective...

and alkaloids

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...

are inducible defenses

Inducible plant defenses against herbivory

Plants and herbivores have co-evolved together for 350 million years. Plants have evolved many defence mechanisms against insect herbivory. Such defences can be broadly classified into two categories: permanent, constitutive defences, and temporary, inducible defences...

which act similarly to defensive compounds produced by plants and are highly toxic to a wide variety of phytophagous insects as well as mammalian herbivores. Peramine occurs widely in endophyte-associated grasses and may also act as a signal to invertebrate herbivores of the presence of more dangerous defensive chemicals. Terpenoids

Terpenoid

The terpenoids , sometimes called isoprenoids, are a large and diverse class of naturally occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures that differ from one another not only in...

and ketones

Ketone

In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

have been linked to protection from specialist and generalist herbivores (both insect and vertebrate) across the higher plants.

Generalist herbivores are more likely than specialists to be negatively affected by the defense chemicals that endophytes produce because they have, on average, less resistance to these specific, qualitative defenses. Among the chewing insects, infection by mycorrhizae can actually benefit specialist feeders even if it negatively affects generalists. The overall pattern of effects on insect herbivores seems to support this, with generalist mesophyll feeders experiencing negative effects of host infection, although phloem

Phloem

In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...

feeders appear to be affected little by fungal defenses.

Secondary metabolites may also affect the behaviour of natural enemies of herbivorous species in a multi-trophic

Trophic level

The trophic level of an organism is the position it occupies in a food chain. The word trophic derives from the Greek τροφή referring to food or feeding. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps an organism...

defense/predation association. For instance, terpenoid production attracts natural enemies of herbivores to damaged plants. These enemies can reduce numbers of invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

herbivores substantially and may not be attracted in the absence of endophytic symbionts. Multi-trophic interactions can have cascading consequences for the entire plant community

Community (ecology)

In ecology, a community is an assemblage of two or more populations of different species occupying the same geographical area. The term community has a variety of uses...

, with the potential to vary widely depending on the combination of fungal species infecting a given plant and the abiotic conditions.

Altered nutrient content

Due to the inherently nutrient-exchange based economy of the plant-endophyte association, it is not surprising that infection by fungi directly alters the chemical composition of plants, with corresponding impacts on their herbivores. Endophytes frequently increase apoplastic

Apoplast

Within a plant, the apoplast is the free diffusional space outside the plasma membrane. It is interrupted by the Casparian strip in roots, air spaces between plant cells and the cuticula of the plant....

carbohydrate

Carbohydrate

A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...

concentration, altering the C:N ratio of leaves and making them a less efficient source of protein. This effect can be compounded when the fungus also uses plant nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

to form N-based secondary metabolites such as alkaloids. For example, the thistle gall fly (Urophora cardui) experiences reduced performance on plants infected with endophytic fungi due to the decrease in N-content and ability to produce large quantities of high-quality gall tissue

Gall

Galls or cecidia are outgrowths on the surface of lifeforms caused by invasion by other lifeforms, such as parasites or bacterial infection. Plant galls are abnormal outgrowths of plant tissues and can be caused by various parasites, from fungi and bacteria, to insects and mites...

. Additionally, increased availability of limiting nutrients to plants improves overall performance and health, potentially increasing the ability of infected plants to defend themselves.

Herbivory prevention

Studies of fungal infection consistently reveal that plants with endophytes are less likely to suffer substantial damage, and herbivores feeding on infected plants are less productive

Productivity (ecology)

In ecology, productivity or production refers to the rate of generation of biomass in an ecosystem. It is usually expressed in units of mass per unit surface per unit time, for instance grams per square metre per day. The mass unit may relate to dry matter or to the mass of carbon generated...

. There are multiple modes through which endophytic fungi reduce insect herbivore damage, including avoidance (deterrence), reduced feeding, reduced development rate, reduced growth and/or population growth

Population growth

Population growth is the change in a population over time, and can be quantified as the change in the number of individuals of any species in a population using "per unit time" for measurement....

, reduced survival and reduced oviposition. Vertebrate

Vertebrate

Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

herbivores such as birds, rabbits and deer show the same patterns of avoidance and reduced performance. Even below-ground herbivores such as nematodes

Nematode

The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

and root-feeding insects are reduced by endophyte infection. The strongest evidence for anti-herbivore benefits of fungal endophytes come from studies of herbivore populations being extirpated

Local extinction

Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...

when allowed to feed only on infected plants. Examples of local extinction have been documented in crickets, larval armyworms and flour beetles.

Yet chemical defenses produced by fungal endophytes are not universally effective, and numerous insect herbivores are unaffected by a given compound at one or more life history stages; larval stages are often more susceptible to toxins than adults. Even endophytes which purportedly provide some defense benefit to their hosts such as the Neotyphidium partner of many grass species in the alpine tundra

Alpine tundra

Alpine tundra is a natural region that does not contain trees because it is at high altitude. Alpine tundra is distinguished from arctic tundra, because alpine soils are generally better drained than arctic soils...

do not always lead to avoidance or ill-effects on herbivores due to spatial variation in levels of consumption.

Mutualism-pathogenicity continuum

Not all endophytic symbioses confer protection from herbivores – only some species associations act as defense mutualisms. The difference between a mutualistic endophyte and a pathogenic one can be indistinct and dependent on interactions with other species or environmental conditions. Some fungi which are pathogens in the absence of herbivores may become beneficial under high levels of insect damage, such as species which kill plant cells in order to make nutrients available for their own growth, thereby altering nutritional content of leaves and making them a less desirable foodstuff. Some endomycorrhizae may provide defense benefits but at the cost of lost reproductive potential by rendering grasses partially sterile

Sterility (physiology)

Sterility is the physiological inability to effect sexual reproduction in a living thing, members of whose kind have been produced sexually. The term may be used in reference to* types of organism, such as the mule, a sterile hybrid;...

with their own fungal reproductive structures taking precedence. This is not unusual among fungi, as non-endophytic plant pathogens have similar conditionally beneficial effects on defense. Some species of endophyte may be beneficial for the plants in other ways (e.g. nutrient and water uptake) but will provide less benefit as a plant receives more damage and not produce defensive chemicals in response. The effect of one fungus on the plant can be altered when multiple strains of fungi are infecting a given individual in combination.

Some endomycorrhizae may actually promote herbivore damage by making plants more susceptible to it. For example, some oak fungal endophytes are positively correlated with the levels of damage from leaf miners (Cameraria spp.), although negatively correlated with number of larvae present due to a reduction of oviposition on infected plants, which partially mitigates the higher damage rate. This continuum between mutualism and pathogenicity of endophytic fungi has major implications for plant fitness depending on the species of partners available in a given environment; mutualist status is conditional in a way similar to pollination

Pollination

Pollination is the process by which pollen is transferred in plants, thereby enabling fertilisation and sexual reproduction. Pollen grains transport the male gametes to where the female gamete are contained within the carpel; in gymnosperms the pollen is directly applied to the ovule itself...

and can shift from one to the other just as frequently.

Fitness and competitive ability

Fungal endophytes which provide defensive services to their host plants may exert selective pressures

Selection

In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...

favouring association through enhanced fitness

Fitness (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...

relative to uninfected hosts. The fungus Neotyphodium spp. infects grasses and increases fitness under conditions with high levels of interspecific competition

Interspecific competition

Interspecific competition, in ecology, is a form of competition in which individuals of different species compete for the same resource in an ecosystem...

. It does this through a combination of benefits including anti-herbivore defenses and growth promoting factors. The customary assumption that plant growth promotion is the main way fungal mutualists improve fitness under attack from herbivores is changing; alteration of plant chemical composition and induced resistance are now recognized as factors of great importance in improving competitive ability and fecundity. Plants undefended by chemical or physical means at certain points in their life histories have higher survival rates when infected with beneficial endophytic fungi. The general trend of plants infected with mutualistic fungi outperforming uninfected plants under moderate to high herbivory exerts selection for higher levels of fungal association as herbivory levels increase. Unsurprisingly, low to moderate levels of herbivore damage also increases the levels of infection by beneficial endophytic fungi.

In some cases the symbiosis between fungus and plant reaches a point of inseparability; fungal material is transmitted vertically from the maternal parent plant to seeds, forming a near-obligate mutualism. Because seeds are an important aspect of both fecundity and competitive ability for plants, high germination rates and seedling survival increase lifetime fitness. When fitness of plant and fungus become tightly intertwined, it is in the best interest of the endophyte to act in a manner beneficial to the plant, pushing it further toward the mutualism end of the continuum. Such effects of seed defense can also occur in dense stands of conspecifics through horizontal transmission of beneficial fungi. Mechanisms of microbial association defense, protecting the seeds rather than the already established plants, can have such drastic impacts on seed survival that they have been recognized to be an important aspect of the larger ‘seed defence theory’.

Climate change

The range of associated plants and fungi may be altered as climate changes

Climate change

Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

, and not necessarily in a synchronous fashion. Plants may lose or gain endophytes, with as of yet unknown impacts on defense and fitness, although generalist species may provide indirect defense in new habitats more often than not. Above-ground and below-ground associations can be mutual drivers of diversity, so altering the interactions between plants and their fungi may also have drastic effects on the community at large, including herbivores. Changes in distribution may bring plants into competition

Competition (biology)

Competition is an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both is required. Competition both within and between species is an important topic in ecology, especially community ecology...

with previously established local species, making the fungal community – and particularly the pathogenic role of fungus – important in determining outcomes of competition with non-native invasive species

Invasive species

"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....

. As carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

levels rise, the amplified photosynthesis will increase the pool of carbohydrates available to endophytic partners, potentially altering the strength of associations. Infected C3 plants

C3 carbon fixation

carbon fixation is a metabolic pathway for carbon fixation in photosynthesis. This process converts carbon dioxide and ribulose bisphosphate into 3-phosphoglycerate through the following reaction:...

show greater relative growth rate under high CO2 conditions compared to uninfected plants, and it is possible that the fungi drive this pattern of increased carbohydrate production.

Levels of herbivory may also increase as temperature and carbon dioxide concentrations rise. However, should plants remain associated with their current symbiotic fungi, evidence suggests that the degree of defense afforded them should not be altered. Although the amount of damage caused by herbivores frequently increases under elevated levels of atmospheric CO2, the proportion of damage remains constant when host plants are infected by their fungal endophytes. The change in Carbon-Nitrogen ratio will also have important consequences for herbivores. As carbohydrate levels increase within plants, relative nitrogen content will fall, having the dual effects of reducing nutritional benefit per unit biomass

Biomass

Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

and also lowering concentrations of nitrogen-based defenses such as alkaloids.

Early recognition

The effects of endophytic fungi on the chemical composition of plants have been known by humans for centuries in the form of poisoning and disease as well as medicinal uses. Especially noted were impacts on agricultural products and livestock. Recognition and study of the mutualism did not begin in earnest until the 1980s when early studies on the impacts of alkaloids on animal herbivory confirmed their importance as agents of deterrence. Biologists began to characterize the diversity of endophytic mutualists through primitive techniques such as isozyme

Isozyme

Isozymes are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. These enzymes usually display different kinetic parameters Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. These enzymes...

analysis and measuring the effects of infection on herbivores. Basic descriptive accounts of these previously neglected species of fungus became a major goal for mycologists

Mycology

Mycology is the branch of biology concerned with the study of fungi, including their genetic and biochemical properties, their taxonomy and their use to humans as a source for tinder, medicinals , food and entheogens, as well as their dangers, such as poisoning or...

, and a lot of research focus shifted to associates of the grass family (Poaceae

Poaceae

The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...

) in particular, because of the large number of species which represent economically important commodities to humans.

Recent advances and future directions

In addition to continuing descriptive studies of the effects of the effects of infection by defense mutualist endophytes, there has been a sharp increase in the number of studies which delve further into the ecology

Ecology

Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

of plant-fungus associations and especially their multi-trophic impacts. The processes by which endophytic fungi alter plant physiology

Physiology

Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

and volatile chemical

Volatile organic compound

Volatile organic compounds are organic chemicals that have a high vapor pressure at ordinary, room-temperature conditions. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and...

levels are virtually unknown, and limited current results show a lack of consistency under differing environmental conditions, especially differing levels of herbivory. Studies comparing the relative impacts of mutualistic endophytes on inducible defenses and tolerance show a central function of infection in determining both responses to herbivore damage. On the whole, molecular

Molecular biology

Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

mechanisms behind endophyte-mediated plant defense has been an increasing focus of research

Research

Research can be defined as the scientific search for knowledge, or as any systematic investigation, to establish novel facts, solve new or existing problems, prove new ideas, or develop new theories, usually using a scientific method...

over the past ten years.

Since the beginning of the biotechnology

Biotechnology

Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...

revolution, much research has been also focused on using genetically modified endophytes to improve plant yields and defensive properties. The genetic basis of response to herbivory is being explored in tall fescue, where it appears the production of jasmonic acid

Jasmonic acid

Jasmonic acid is derived from the fatty acid linolenic acid. It is a member of the jasmonate class of plant hormones. It is biosynthesized from linolenic acid by the octadecanoid pathway....

may play a role in downregulation of the host plant’s chemical defense pathways when a fungal endophyte is present. In some cases, fungi that are closely associated with their hosts have transferred genes

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

for secondary metabolite production to the host genome

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

, which could help to explain multiple origins of chemical defenses within the phylogeny of various groups of plants. This represents an important line of inquiry to pursue, especially in regards to understanding the chemical pathways that can be utilized in biotechnological applications.

Agriculture and livestock

The secondary chemicals produced by endophytic fungi when associated with their host plants can be very harmful to mammals including livestock and humans, causing more than 600 million dollars in losses due to dead livestock every year. For example, the ergot alkaloids produced by Claviceps spp

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...

. have been dangerous contaminants of rye crops for centuries. When not lethal, defense chemicals produced by fungal endophytes may lead to lower productivity in cows and other livestock feeding on infected forage

Forage

Forage is plant material eaten by grazing livestock.Historically the term forage has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also used more loosely to include similar plants cut for fodder and carried to the animals, especially...

. Reduced nutritional quality of infected plant tissue also lowers the performance of farm animals, compounding the effect of reduced feed uptake when provided with infected plant matter. Reduced frequency of pregnancy and birth has also been reported in cattle and horses fed with infected forage. Consequently, the dairy and meat-production industries must endure substantial economic losses.

Fungal resistance to herbivores represents an environmentally sustainable

Sustainability

Sustainability is the capacity to endure. For humans, sustainability is the long-term maintenance of well being, which has environmental, economic, and social dimensions, and encompasses the concept of union, an interdependent relationship and mutual responsible position with all living and non...

alternative to pesticides

Pesticide

Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

that has experienced reasonable success in agricultural applications. The organic farming industry has embraced mycorrhizal symbionts as one tool for improving yields and protecting plants from damage. Infected crops of soybean

Soybean

The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...

, ribwort plantain, cabbage, banana, coffee bean plant and tomato all show markedly lower rates of herbivore damage compared to uninfected plants. Endophytic fungi show great promise as a means of indirect biocontrol

BioControl

BioControl is a peer-reviewed scientific journal published by Springer Science+Business Media covering all aspects of basic and applied research in biological control of invertebrate, vertebrate, and weed pests, and plant diseases. The journal was established in 1956 as Entomophaga and published by...

in large-scale agricultural applications. The potential for biotechnology to improve crop populations through inoculation

Inoculation

Inoculation is the placement of something that will grow or reproduce, and is most commonly used in respect of the introduction of a serum, vaccine, or antigenic substance into the body of a human or animal, especially to produce or boost immunity to a specific disease...

with modified fungal strains could reduce toxicity to livestock and improve yields of human-consumed foods. The endophyte, either with detrimental genes removed or beneficial new genes added, is used as a surrogate host to transform the crops genetically. An endophyte of ryegrass has been genetically transformed in this way and used successfully to deter herbivores.

Understanding how to mediate top-down effects on crop populations caused by the enemies of herbivores as well as bottom-up effects of chemical composition in infected plants has important consequences for the management of agricultural industries. The selection of endophytes for agricultural use must be careful and consideration must be paid to the specific impacts of infection on all species of pest and predators or parasites, which may vary on a geographic scale. The union of ecological and molecular techniques to increase yield without sacrificing the health of the local or global environment is a growing area of research.

Pharmaceutical

Many secondary metabolites from endophyte-plant interactions have also been isolated and used in raw or derived forms to produce a variety of drugs

DRUGS

Destroy Rebuild Until God Shows are an American post-hardcore band formed in 2010. They released their debut self-titled album on February 22, 2011.- Formation :...

treating many conditions. The toxic properties of ergot alkaloids also make them useful in the treatment of headaches and throughout the process of giving birth by inducing contractions and stemming hemorrages. Drugs used to treat Parkinson's Disease have been created from isolates of ergot toxins, although health risks may accompany their use. Ergotamine has also been used to synthesize lysergic acid diethylamide because of its chemical similarity to lysergic acid

Lysergic acid

Lysergic acid, also known as D-lysergic acid and -lysergic acid, is a precursor for a wide range of ergoline alkaloids that are produced by the ergot fungus and some plants. Amides of lysergic acid, lysergamides, are widely used as pharmaceuticals and as psychedelic drugs...

. The generally chemically-based defense properties of endophytic fungi make them a perfect group of organisms to search for new antibiotic

Antibiotic

An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...

compounds within, as other fungi have in the past yielded such useful drugs as penicillin

Penicillin

Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....

and streptomycin

Streptomycin

Streptomycin is an antibiotic drug, the first of a class of drugs called aminoglycosides to be discovered, and was the first antibiotic remedy for tuberculosis. It is derived from the actinobacterium Streptomyces griseus. Streptomycin is a bactericidal antibiotic. Streptomycin cannot be given...

and plants use their antibiotic qualities as a defense against pathogens.

External Links

Mycorrhizal Associations: The Web Resource - Comprehensive illustrations and lists of mycorrhizal and nonmycorrhizal plants and fungi
International Mycorrhiza Society
Mycorrhizal Literature Exchange - Database of abstracts, reviews, books, theses and dissertations hosted by the University of Tennessee
Plant Defense Systems and Medicinal Botany - Explanations of plant defensive chemicals and their use by humans

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Diversity of endophytic associations

Secondary metabolite production

Altered nutrient content

Herbivory prevention

Mutualism-pathogenicity continuum

Fitness and competitive ability

Climate change

Early recognition

Recent advances and future directions

Agriculture and livestock

Pharmaceutical

See also

External Links