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 cycle without causing apparent disease. Endophytes are ubiquitous and have been found in all species of plants studied to date; however, most of the endophyte/plant relationships are not well understood. Some endophytes may enhance host growth, nutrient acquisition and may improve the plant's ability to tolerate abiotic stresses, such as drought, and enhance resistance to insects, plant pathogens and herbivores. As often with other organisms associated with plants such as mycorrhizal fungus, endophytes gain carbon from their association with the plant host.

History[edit]

Endophytes were first described by the German botanist Heinrich Friedrich Link in 1809. They were thought to be plant parasitic fungi and they were later termed as "microzymas" by the French scientist Béchamp. There was a belief that plants were healthy under sterile conditions and it was not until 1887 when Victor Galippe discovered bacteria normally occurring in the inside of plant tissues.[1]

Transmission[edit]

Endophytes may be transmitted either vertically (directly from parent to offspring) or horizontally (among individuals).[2] Vertically transmitted fungal endophytes are typically considered clonal and transmit via fungal hyphae penetrating the embryo within the host’s seeds, while reproduction of the fungi through asexual conidia or sexual spores leads to horizontal transmission, where endophytes may spread between plants in a population or community.[3]

Symbiosis[edit]

Most endophyte/plant relationships are not well understood.[4]

Endophytes and plants often engage in mutualism, with endophytes primarily aiding in the health and survival of the host plant with issues such as pathogens and disease, water stress, heat stress, nutrient availability and poor soil quality, salinity, and herbivory.[5] Plant-microbe interactions are not strictly mutualistic, with endophytic fungi potentially becoming pathogens or saprotrophs that only become active and reproduce under specific environmental conditions or when their host plants are stressed or begin to senesce.[6][7]

Endophytes may benefit host plants by preventing pathogenic or parasitic organisms from colonizing them, by extensively colonizing plant tissues and competitively excluding potential pathogens and herbivores.[8][9]

Some fungal and bacterial endophytes have proven to increase plant growth and improve overall plant hardiness.[10]

Diversity[edit]

Endophytic species are very diverse; only a small minority of existing endophytes have been characterized.[11][12]

From within the phylums Basidiomycota and Ascomycota endophytic fungi may be from Hypocreales and Xylariales of the Sordariomycetes (Pyrenomycetes) class or from the class of Loculoascomycetes.[13]

One group of fungal endophytes are the arbusbuclar mycorrhizal fungi involving biotrophic Glomeromycota associated with various plant species.[14]

Bacterial endophytes are polyphyletic, belonging to broad range of taxa, including α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, Firmicutes, Actinobacteria.[15]

Applications[edit]

Biofuel[edit]

The main quality selected for use in biofuel is high productivity. Through the above benefits use of endophytes can potentially increase productivity and allow production to occur on land otherwise unsuitable.[16] Inoculating plants with certain endophytes may provide increased disease or parasite resistance [17] while others may possess metabolic processes that convert cellulose and other carbon sources into "myco-diesel" hydrocarbons and hydrocarbon derivatives.[18] Common species used in biofuel in the US are Zea mays (corn), Salix species (poplars and willows), and sugarcane species.

Environmental remediation[edit]

In restoration ecology, endophytes can assist native species in outcompeting non-native invasive species and, colonizing barren land in secondary ecological succession, and restoring ecosystems degraded by pollutants. As with in biofuel production, in phytoremediation high productivity species are often used. Plants are able to contain, store, potentially break down, and stimulate microorganisms in the soil to break down certain pollutants.[19] With phytoremediation the main challenge is the growth of plants in soil contaminated with organic pollutants and inorganic pollutants such as heavy metals. In this endophytes assist plants in converting pollutants into less biologically harmful forms such as breaking down TCE of PAHs in their metabolic pathways, and assist plants in tolerating higher levels of soil contamination with pollutants such as toluene.[19]

The roots of plant communities to varying degrees help hold soil together by creating a network of roots that trap soil within. This in turn helps prevent soil erosion, stabilizes slopes and prevent landslides, helps prevent desertification in vulnerable areas, and controls pollution into waterways by acting as part of riparian buffers.[20]

Drug discovery[edit]

Endophytes can produce a wide variety of compounds that might be useful as lead compounds in drug discovery.[21][22] Certain fungal endophyte secondary metabolites have anti-fungal, anti-microbial, anti-viral, anti-oxidant, and anti-cancer properties; examples of this include taxol, torreyanic acid, exopolysaccharides, and solamargine.[23] Manipulations of a plant's endosymbiots can also affect plant development, growth and ultimately the quality and quantity of compounds harvested from the plant.[6]

Agriculture[edit]

Among the many promising applications of endophytic microbes are those intended to increase agricultural use of endophytes to produce crops that grow faster and are more resistant and hardier than crops lacking endophytes.[24] Epichloë endophytes are being widely used commercially in turf grasses to enhance the performance of the turf and its resistance to biotic and abiotic stresses.[25] Piriformospora indica is an interesting endophytic fungus of the order Sebacinales, the fungus is capable of colonising roots and forming symbiotic relationship with many plants.[26]

See also[edit]

References[edit]

  1. ^ Hardoim, Pablo R.; Van Overbeek, Leonard S.; Berg, Gabriele; Pirttilä, Anna Maria; Compant, Stéphane; Campisano, Andrea; Döring, Matthias; Sessitsch, Angela (2015). "The Hidden World within Plants: Ecological and Evolutionary Considerations for Defining Functioning of Microbial Endophytes". Microbiology and Molecular Biology Reviews. 79 (3): 293. PMID 26136581. doi:10.1128/MMBR.00050-14. 
  2. ^ Suryanarayanan, Trichur S. (2013-12-01). "Endophyte research: going beyond isolation and metabolite documentation". Fungal Ecology. 6 (6): 561–568. doi:10.1016/j.funeco.2013.09.007. 
  3. ^ Tadych, Mariusz; Bergen, Marshall S.; White, James F. (2014-03-01). "Epichloë spp. associated with grasses: new insights on life cycles, dissemination and evolution". Mycologia. 106 (2): 181–201. PMID 24877257. doi:10.3852/106.2.181. 
  4. ^ Saunders, Megan; Glenn, Anthony E.; Kohn, Linda M. (2010-09-01). "Exploring the evolutionary ecology of fungal endophytes in agricultural systems: using functional traits to reveal mechanisms in community processes". Evolutionary Applications. 3 (5–6): 525–537. ISSN 1752-4571. PMC 3352505Freely accessible. PMID 25567944. doi:10.1111/j.1752-4571.2010.00141.x. 
  5. ^ Hardoim, Pablo R.; Overbeek, Leonard S. van; Berg, Gabriele; Pirttilä, Anna Maria; Compant, Stéphane; Campisano, Andrea; Döring, Matthias; Sessitsch, Angela (2015-09-01). "The Hidden World within Plants: Ecological and Evolutionary Considerations for Defining Functioning of Microbial Endophytes". Microbiology and Molecular Biology Reviews. 79 (3): 293–320. ISSN 1092-2172. PMC 4488371Freely accessible. PMID 26136581. doi:10.1128/MMBR.00050-14. 
  6. ^ a b Jia, Min; Chen, Ling; Xin, Hai-Liang; Zheng, Cheng-Jian; Rahman, Khalid; Han, Ting; Qin, Lu-Ping (2016-06-09). "A Friendly Relationship between Endophytic Fungi and Medicinal Plants: A Systematic Review". Frontiers in Microbiology. 7: 906. ISSN 1664-302X. PMC 4899461Freely accessible. PMID 27375610. doi:10.3389/fmicb.2016.00906. 
  7. ^ Rai, Mahendra; Agarkar, Gauravi (2013-11-10). "Plant–fungal interactions: What triggers the fungi to switch among lifestyles?". Critical Reviews in Microbiology. 42 (3): 428–438. ISSN 1040-841X. PMID 25383649. doi:10.3109/1040841X.2014.958052. 
  8. ^ Kuldau, G.; Bacon, C. (2008-07-01). "Clavicipitaceous endophytes: Their ability to enhance resistance of grasses to multiple stresses". Biological Control. Special Issue: Endophytes. 46 (1): 57–71. doi:10.1016/j.biocontrol.2008.01.023. 
  9. ^ Zabalgogeazcoa, I. (2008-02-01). "Fungal endophytes and their interaction with plant pathogens: a review". Spanish Journal of Agricultural Research. 6 (S1): 138–146. ISSN 2171-9292. doi:10.5424/sjar/200806S1-382. 
  10. ^ Hardoim, Pablo R.; van Overbeek, Leo S.; Elsas, Jan Dirk van (2008-01-10). "Properties of bacterial endophytes and their proposed role in plant growth". Trends in Microbiology. 16 (10): 463–471. ISSN 0966-842X. PMID 18789693. doi:10.1016/j.tim.2008.07.008. 
  11. ^ Suman, Archna; Yadav, Ajar Nath; Verma, Priyanka (2016-01-01). "Endophytic Microbes in Crops: Diversity and Beneficial Impact for Sustainable Agriculture". In Singh, Dhananjaya Pratap; Singh, Harikesh Bahadur; Prabha, Ratna. Microbial Inoculants in Sustainable Agricultural Productivity. Springer India. pp. 117–143. ISBN 9788132226451. doi:10.1007/978-81-322-2647-5_7. 
  12. ^ Rodriguez, R. J.; White, J. F.; Arnold, A. E.; Redman, R. S. (2009). "Fungal endophytes: diversity and functional roles". The New Phytologist. 182 (2): 314–330. ISSN 1469-8137. PMID 19236579. doi:10.1111/j.1469-8137.2009.02773.x. 
  13. ^ Unterseher, Martin (2011-01-01). Pirttilä, Anna Maria; Frank, A. Carolin, eds. Endophytes of Forest Trees. Forestry Sciences. Springer Netherlands. pp. 31–46. ISBN 978-94-007-1598-1. doi:10.1007/978-94-007-1599-8_2. 
  14. ^ van der Heijden, Marcel G. A.; Martin, Francis M.; Selosse, Marc-André; Sanders, Ian R. (2015-03-01). "Mycorrhizal ecology and evolution: the past, the present, and the future". The New Phytologist. 205 (4): 1406–1423. ISSN 1469-8137. PMID 25639293. doi:10.1111/nph.13288. 
  15. ^ Miliute, Inga; Buzaite, Odeta; Baniulis, Danas; Stanys, Vidmantas (2015). "Bacterial endophytes in agricultural crops and their role in stress tolerance: a review". Zemdirbyste-Agriculture. 102 (4): 465–478. doi:10.13080/z-a.2015.102.060. 
  16. ^ Compant, Stéphane; Clément, Christophe; Sessitsch, Angela (2010-05-01). "Plant growth-promoting bacteria in the rhizo- and endosphere of plants: Their role, colonization, mechanisms involved and prospects for utilization". Soil Biology and Biochemistry. 42 (5): 669–678. doi:10.1016/j.soilbio.2009.11.024. 
  17. ^ "University of Rhode Island GreenShare Factsheets: Endopyhte-Enhanced Grasses". Archived from the original on 2006-03-12. Retrieved June 14, 2009. 
  18. ^ Strobel GA, Knighton B, Kluck K, et al. (November 2008). "The production of myco-diesel hydrocarbons and their derivatives by the endophytic fungus Gliocladium roseum (NRRL 50072)". Microbiology. 154 (11): 3319–28. PMID 18957585. doi:10.1099/mic.0.2008/022186-0. 
  19. ^ a b Altman, Arie; Hasegawa, Paul, eds. (2011). Plant Biotechnology and Agriculture: Prospects for the 21st Century. Academic press. pp. 309–328. ISBN 9780123814661. OCLC 858878994. 
  20. ^ Wu, Tien H. (2013-01-14). "Root reinforcement of soil: review of analytical models, test results, and applications to design". Canadian Geotechnical Journal. 50 (3): 259–274. ISSN 0008-3674. doi:10.1139/cgj-2012-0160. 
  21. ^ Nisa, Humeera; Kamili, Azra N.; Nawchoo, Irshad A.; Shafi, Sana; Shameem, Nowsheen; Bandh, Suhaib A. (2015-05-01). "Fungal endophytes as prolific source of phytochemicals and other bioactive natural products: A review". Microbial Pathogenesis. 82: 50–59. doi:10.1016/j.micpath.2015.04.001. 
  22. ^ Sarasan, M; Puthumana, J; Job, N; Han, J; Lee, JS; Philip, R (5 April 2017). "Marine algicolous endophytic fungi- A promising drug resource of the era". Journal of microbiology and biotechnology. PMID 28376612. doi:10.4014/jmb.1701.01036 (inactive 2017-06-18). 
  23. ^ Pandey, Pramod Kuma; Singh, Siddhartha; Yadav, Raj Naraian Singh; Singh, Amit Kumar; Singh, M. Chandra Kumar (2014). "Fungal endophytes: promising tools for pharmaceutical science" (PDF). International Journal of Pharmaceutical Sciences Review & Research. 25: 128–138. 
  24. ^ Bacon, Charles W.; Hinton, Dorothy M. (2014-01-01). Verma, Vijay C.; Gange, Alan C., eds. Microbial Endophytes: Future Challenges. Springer India. pp. 441–451. ISBN 978-81-322-1574-5. doi:10.1007/978-81-322-1575-2_22. 
  25. ^ Meyer, William; Torres, Monica; White, James (2012). Stier, J.; Horgan, B.; Bonos, S., eds. Chapter 20: Biology and Applications of Fungal Endophytes in Turfgrasses. In book: Agronomy Monograph 56. Turfgrass: Biology, Use, and Management. American Society of Agronomy. pp. Chapter 20. 
  26. ^ Qiang, X; Weiss, M; Kogel, KH; Schäfer, P (June 2012). "Piriformospora indica-a mutualistic basidiomycete with an exceptionally large plant host range.". Molecular plant pathology. 13 (5): 508–18. PMID 22111580. doi:10.1111/j.1364-3703.2011.00764.x.