Fungal Endophytes: Drought Tolerance in Plants

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It has been estimated that over 80% of terrestrial plants form a symbiotic association with fungi.[1] Fungal endophytes have played an essential role in the evolution of land plants and remain an important component of terrestrial ecosystems. In these mutualistic associations, fungi may benefit their host plant by acquiring nutrients, increasing plant biomass, and conferring tolerance to biotic and abiotic stresses. Studies show that symbiotic fungi can enhance drought, salt, and soil temperature tolerance of their host plant in addition to increasing its resistance to parasitic fungi and herbivores. These habitat-adapted symbioses enable plants to thrive in harsh conditions where they would otherwise not be able to grow.

It is hypothesized that phototroph-fungi associations enabled plants to first colonize land. The mutualistic association of algae and fungi could have helped them avoid desiccation, damaging solar radiation, and more extreme temperatures.[2] Fungal endophytes today colonize a variety of both monocot and eudicot plants which suggests this symbiosis predates the monocot-dicot split that occured 140-150 Myr ago.[3]

Fungal endophytes have many potential applications in agriculture and conservation, yet there is still much that is not known about plant-fungi symbiosis and the mechanisms behind it. Fungal endophytes alter plants’ growth, development, and root morphology to reduce water consumption and increase nutrient uptake. This may be used to increase crop yield in arid climates and mitigate the negative effects of climate change.

Classes of Fungal Endophytes

Clavicipitaceous Endophytes (C-endophytes)

Class 1

C-endophytes infect the plant shoots of some grasses, form systemic intercellular infections, and are passed on through vertical and horizontal transmission.[4] Many produce alkaloids to protect their host plant from herbivory by insects and mammals, and studies have shown them to confer drought and metal tolerance.[4][5] Endophytes may increase the development of root systems or the length of root hairs.[4]

Nonclavicipitaceous Endophytes (NC-endophytes)

Class 2

Class 2 endophytes are usually found in the roots, stem, or leaves of their hosts.[4] They can be transmitted either vertically through the seed coat or horizontally. [4] They can confer habitat-specific stress tolerance to their hosts, and they infect a higher percentage of plants in high-stress environments.[4]

Class 3 and 4

Class 3 colonizes the shoot of plants while Class 4 colonizes plant roots.[4] Few studies have been performed on Classes 3 and 4 endophytes, and little is known about their ecological role and their ability to confer tolerance.

Further Reading

[Sample link] Ebola Hemorrhagic Fever—Centers for Disease Control and Prevention, Special Pathogens Branch-->

References

|[1][Smith, S., Read, D., 1997: Mycorrhizal symbiosis, 2nd edn., Academy Press, San Diego. ]
|[2]Selosse, M-A, and F. Le Tacon. "The Land Flora: A Phototroph-Fungus Partnership?" Trends in Ecology & Evolution 13.1 (1998): 15-20. Print.
|[3] Shu-Miaw C., Chien-Chang C., Hsin-Liang C., Wen-Hsiung L."Dating the Monocot–Dicot Divergence and the Origin of Core Eudicots Using Whole Chloroplast Genomes". "Journal of Molecular Evolution". 2004. Volume 58, p. 424-441
|[4]Rodriguez, R. J., et al. "Fungal Endophytes: Diversity and Functional Roles." New Phytologist 182.2 (2009): 314-30. Print.
|[5] Koulman, Albert, et al. "Peramine and Other Fungal Alkaloids are Exuded in the Guttation Fluid of Endophyte-Infected Grasses." Phytochemistry 68.3 (2007): 355-60. Print.

Edited by (Sarah Barnes), a student of Nora Sullivan in BIOL168L (Microbiology) in The Keck Science Department of the Claremont Colleges Spring 2014.