endophyte

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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 are not well understood. Many economically important forage and turfgrasses (e.g., Festuca spp., Lolium spp.) carry fungal endophytes (Neotyphodium spp.) which may improve the ability of these grasses to tolerate abiotic stresses such as drought, as well as improve their resistance to insect and mammalian herbivores. ^[1]

Transmission

Endophytes may be transmitted either vertically (directly from parent to offspring) or horizontally (from individual to unrelated individual). Vertically transmitted fungal endophytes are asexual and transmit via fungal hyphae penetrating the host’s seeds (e.g. Neotyphodium). Since their reproductive fitness is intimately tied to that of their host plant, these fungi are often mutualistic. Conversely, horizontally transmitted fungal endophytes are sexual and transmit via spores that can be spread by wind and/or insect vectors. Since they spread in a similar way to pathogens, horizontally transmitted endophytes are often closely related to pathogenic fungi, though they are not pathogenic themselves.

Endophyte-Host Relationship

Endophytes may benefit host plants by preventing pathogenic organisms from colonizing them. Extensive colonization of the plant tissue by endophytes creates a "barrier effect", where the local endophytes outcompete and prevent pathogenic organisms from taking hold. Endophytes may also produce chemicals which inhibit the growth of competitors, including pathogenic organisms. The presence of fungal endophytes has been shown to cause higher rates of water loss in leaves.

Use

The wide range of compounds produced by endophytes have been shown to combat pathogens and even cancers in animals including humans. One notable endophyte with medicinal benefits to humans was discovered by Dr. Gary Strobel, produces taxol, and is found within the Pacific Yew tree. Endophytes are also being investigated for roles in agriculture and biofuels production. Inoculating crop plants with certain endophytes may provide increased disease or parasite resistance ^[1] while others may possess metabolic processes that convert cellulose and other carbon sources into "myco-diesel" hydrocarbons and hydrocarbon derivatives.^[2]

It is speculated that there may be many thousands of endophytes useful to mankind but since there are few scientists working in this field, and since forests and areas of biodiversity are rapidly being destroyed, many useful endophytes for curing disease might be permanently lost for medicinal use before they are discovered. The effects of climate change on endophytes is being investigated. Studies of plants grown at different climates or at increased carbon dioxide levels have different distributions of endophytic species

Identification

While many endophytes are known to colonize multiple species of plants, some are host specific. Endophytic species are very diverse; it is thought that only a small minority of all existing endophytes have been characterized. A single leaf of a plant can harbor many different species of endophytes, both bacterial and fungal.

Endophytes can be identified in several ways, usually through amplifying and sequencing a small piece of DNA. Some endophytes can be cultured from a small piece of their host plant in an appropriate growth medium. Not all endophytes present can be cultured in this way because amplification ground up plant tissue using fungal or bacterial specific primers has revealed the existence cryptic species. Grass leaf endophytes can be seen as coiled tubes of hyphae under the microscope at 400X following clearing of the leaf sheaths in ethanol and staining with aniline blue.

References

• Cheplick, G.P. and S.H. Faeth. 2009. Ecology and Evolution of the Grass-Endophyte Symbiosis. Oxford University Press, Oxford.
• Strobel G et al. Microbiology 154 (2008), 3319-3328; DOI 10.1099/mic.0.2008/022186-0

External links

• "Endophytes and their promise for new medicines and products for agriculture and industry". Jewels of the Jungle. http://www.jewelsofthejungleweb.com/Endophytes.html. Retrieved 2008-03-12.