Grasses and endophytic fungi: Difference between revisions

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The endophytic fungi also receive benefits including greater access to nutrients, protection from desiccation, protection from surface feeding insects, and protection from parasitic fungi and competition among other microbes(1).  Depending on both the fungal and grass species, the relationship can be very specific or have a wide range of possible host grass plants.  
The endophytic fungi also receive benefits including greater access to nutrients, protection from desiccation, protection from surface feeding insects, and protection from parasitic fungi and competition among other microbes(1).  Depending on both the fungal and grass species, the relationship can be very specific or have a wide range of possible host grass plants.  


Most symbiotic relationships are pleitropic (balanced) in the Epichloe and Neotyphodium genera.  The other symbiotic relationships include nonpathogenic symbionts that transmit vertically by systematic infection of seed(asexual).  This type of symbiosis is highly beneficial to the host.  On the opposite end of the spectrum, there are antagonistic symbionts and transmit horizontally (contagious) and suppress host seed production(sexual).


===Influence on other organisms===
===Influence on other organisms===

Revision as of 08:14, 6 April 2011

This student page has not been curated.

Introduction

The relationship between certain grasses and endophytic [1] fungi is symbiotic [2]. The most common benefit that the plant receives from the endophytic fungi is increased resistance to herbivores and other environmental stresses (2). The endophytic fungi produce toxic alkaloids [3] that can deter herbivores or reduce the performance of the herbivore(article 2). The grass provides food and shelter for the fungi in return (fungus wiki 142). The discovery of this relationship occurred when cattle grazing on the infected grass developed delirium and “livestock staggering”(2).

Biological interaction

The relationship between endophytic fungi and grasses is systematically symbiotic. The defensive and most successful fungal endophytes produce no visble effects in plants. Even so, there are a variety of advantages the grass receives from the fungi. This includes enhanced insect herbivory resistance, fungal disease resistance, enhanced vegetative growth, and increased drought tolerance.

The endophytic fungi also receive benefits including greater access to nutrients, protection from desiccation, protection from surface feeding insects, and protection from parasitic fungi and competition among other microbes(1). Depending on both the fungal and grass species, the relationship can be very specific or have a wide range of possible host grass plants.


Influence on other organisms

Mammals

Endophytic Fungi produce alkaloids (ergotoxin and indolediterpenoid tremorgens) that are toxic to mammalian herbivores. The species that most effects mammals are from the genus Neotyphodium. When mammals consume grass infected with the fungi, different neurological effects take place(1)

Cattle that graze on infected tall fescue grass can develop a condition known as "fescue foot". Over a long period of time, blood is reduced to extremities which eventually leads to the tail or hoove rotting off..

When animals graze on perennial rye grass infected by N.lolii, they may develop uncontrollable spasms. Another grass, sleepy grass, contains a Neoptyphodium that causes horses to sleep for two to three days (1).

Insects

Insects react and have different reactions to the toxin, but the overall pattern is that the endophytic fungi promote anti-herbivory benefits in native grasses. The alkaloid toxin that protects against herbivory are lolines and peramines (3).

Microbes

Fungal endophytes, in particluar Neotyphodium, are shown to reduce colonization of arbuscular mycorrhizal fungi on the host (4). Mechanism by which the endophyte reduces colonization is through allelopathic effects. The affect on the mycorrhizal fungi from endophytic fungi is an important process to understand. Mycorrhizae promote plant growth and overall, grassland ecosystems (4).

Niche

Endophytic fungi are distributed in the intercellular portion of the host and restricted to above ground growth (1). This growth occurs in the floret, sheath, stem, and leaf tissues of the developing grass seedling and maturing plant (2). Endophytic fungi are considered an intercellular foliage symbiont and associations are established at the seedling stage and are long-lived. All grass fungal endophytes are capable of growth on a wide range of simple carbon sources. The endophytic fungi need amino acids, simple sugars, and a variety of vitamins to survive and are acquired from the apoplasm of the host (1).

Microbial processes

One of the more important processes involved in the endophytic fungi - grass relationship is the production of alkaloids. There are four different kinds of alkaloids produced, and each have different consequences. The first two, lolines [4] and peramines have no other close chemical relatives. These two toxins protect against herbivory. The other two are ergotoxins [5] and indolediterpenoid tremorgens which are the toxins that affect the mammalian neurological system. These toxins help prevent insect and mammalian herbivory and increases plant growth and vigor. The endphytes must produce stromata in order to reproduce sexually. The stromata helps flow of nutrients from the host to the fungal component of stroma. Plant tissues within the stroma can be modified by the endophytes to increase flow of nutrients into the mycelium (1).

Key Microorganisms

Endophytic fungi are within the family Clavicipitaceae[6]. The most common genera of endophytic fungi include Balansia and Epichloe. All endophytic fungi have hyphal cells that are in intimate contact with the host cells and are intercellular.

Balansia

The genus Balansia became endosymbiotic when the group of the B. claviceps subclade evolved from an episymbiotic ancestor. Work has shown that endophytic Balansia are limited to the Americas.

Epichloe

All species of the genus epichloe are endosymbiotic. Epichloe are important for protection of the hosts under environmental stresses imbosed biotically or abiotically. There are three types of symbionts.

Nonpathogenic

Benign symbionts are highly beneficial to the hosts and only transmit vertically [7]. The symbiont is asexual (Neotyphodium).

Pathogenic

Antagonastic endophytic species transmit horizontally (contagiously). This symbioant completely suppresses host seed production and are sexual.

Pleiotropic

Balanced symbiosis is said to have the most benefits for the host grass. This is a relationship that transmits both vertically and horizontally. The grass and fungas both have a sexual stage and asexual reproductive capabilites.

Current Research

1. "Phytoremediation of an aged petroleum contaminated soil using endophyte infected and non-infected grasses."

This study researches how phytoremediation can help clean petroleum contaminated soils. It uses two grasses that are infected by endophytic fungi to test the degradation of petroleum hydrocarbons in aged petroleum contaminated soil. The research showed that the grasses infected could be more efficient in removal of total petroleum hydrocarbons from contaminated sites (5).

2."Asexual endophytes and associated alkaloids alter arthropod community structure and increase herbivore abundances on a native grass."

Field experiments and population surveys were used to find how endophyte infection and alkaloids influenced the abundances, species richness, and guild structure of arthropods on native grass. This study research sleepygrass (Achnatherum robutum) and found that when alkaloids were produced, there was increased herbivory abundance. This study goes against other findings that have been found in agronomic grass systems. High alkaloid levels may not always mean increased protection against herbivory (6).

3. "Variable effects of endophytic fungus on seedling establishment of fine fescues."

This experiment examined endophytic fungi infected and non infected seeds of two grasses, Festuca rubra and Festuca ovina. The results show that the effects of the endophyte on the grass depends on various factors such as species of grass, genetic background, and the mother plant habitat(7).



References

1. Bacon, Charles W, White, James F., comp. Microbial Endophytes. New York: Marcel Dekker Inc., 2000.

2. http://www.uri.edu/ce/factsheets/sheets/endophyte.html

3. Crawford, Kerri M. et al. "Fungal endophytes of native grasses decrease insect herivore preference and performance." 29 June 2010. Sringer-Verlag 2010.

4. Antunes, P.M. et al. "Even after death the endophytic fungus of Schedonorus phoenix reduces the arbuscular mycorrhizas of other plants." Functional Ecology 2008, 22, 912-918.

5. Jan H. Christensen, et al. "Phytoremediation of an aged petroleum contaminated soil using endophyte infected and non-infected grasses." Chemosphere 81.9 (2010): 1084-1090. Academic Search Premier. EBSCO. Web. 6 Apr. 2011.

6. Jani, Andrea J., Stanley H. Faeth, and Dale Gardner. "Asexual endophytes and associated alkaloids alter arthropod community structure and increase herbivore abundances on a native grass." Ecology Letters 13.1 (2010): 106-117. Academic Search Premier. EBSCO. Web. 6 Apr. 2011.

7. Kari Saikkonen, et al. "Variable effects of endophytic fungus on seedling establishment of fine fescues." Oecologia 159.1 (2009): 49-57. Academic Search Premier. EBSCO. Web. 6 Apr. 2011.


Edited by <Maureen Schwer>, a student of Angela Kent at the University of Illinois at Urbana-Champaign.