Ectomycorrhizal symbiosis: Difference between revisions

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Three main ammonium transporters have been identified in several fungal ECM species: AMT1, AMT2, and AMT3. The former two are high-affinity transporters, meaning their expression is upregulated most in conditions of low ammonium. <ref> [https://doi.org/10.1046/j.1365-2958.2003.03303.x Javelle, Arnaud, Mélanie Morel, Blanca‐Rosa Rodríguez‐Pastrana, Bernard Botton, Bruno André, Anne‐Marie Marini, Annick Brun, and Michel Chalot. "Molecular characterization, function and regulation of ammonium transporters (Amt) and ammonium‐metabolizing enzymes (GS, NADP‐GDH) in the ectomycorrhizal fungus Hebeloma cylindrosporum." Molecular microbiology 47, no. 2 (2003): 411-430.] </ref> Nitrate can also be uptaken by ECM fungi and requires the regulation of nitrate transporters, such as LbNRT2, and nitrate reductase enzymes. <ref> [https://doi.org/10.1111/j.1758-2229.2009.00111.x Kemppainen, Minna J., Maria C. Alvarez Crespo, and Alejandro G. Pardo. "fHANT‐AC genes of the ectomycorrhizal fungus Laccaria bicolor are not repressed by l‐glutamine allowing simultaneous utilization of nitrate and organic nitrogen sources." Environmental microbiology reports 2, no. 4 (2010): 541-553.] </ref> In the presence of ammonium, the nitrate uptake pathway is downregulated due to the fungal preference for ammonium. The oxidative decomposition mechanisms inherited by ECM fungi from their saprotrophic ancestors allow for organic N sources to be used as well. Peptidase secretion is then used to reduce proteins from the soil into smaller peptide products. <ref name="foo" /> <br>
Three main ammonium transporters have been identified in several fungal ECM species: AMT1, AMT2, and AMT3. The former two are high-affinity transporters, meaning their expression is upregulated most in conditions of low ammonium. <ref> [https://doi.org/10.1046/j.1365-2958.2003.03303.x Javelle, Arnaud, Mélanie Morel, Blanca‐Rosa Rodríguez‐Pastrana, Bernard Botton, Bruno André, Anne‐Marie Marini, Annick Brun, and Michel Chalot. "Molecular characterization, function and regulation of ammonium transporters (Amt) and ammonium‐metabolizing enzymes (GS, NADP‐GDH) in the ectomycorrhizal fungus Hebeloma cylindrosporum." Molecular microbiology 47, no. 2 (2003): 411-430.] </ref> Nitrate can also be uptaken by ECM fungi and requires the regulation of nitrate transporters, such as LbNRT2, and nitrate reductase enzymes. <ref> [https://doi.org/10.1111/j.1758-2229.2009.00111.x Kemppainen, Minna J., Maria C. Alvarez Crespo, and Alejandro G. Pardo. "fHANT‐AC genes of the ectomycorrhizal fungus Laccaria bicolor are not repressed by l‐glutamine allowing simultaneous utilization of nitrate and organic nitrogen sources." Environmental microbiology reports 2, no. 4 (2010): 541-553.] </ref> In the presence of ammonium, the nitrate uptake pathway is downregulated due to the fungal preference for ammonium. The oxidative decomposition mechanisms inherited by ECM fungi from their saprotrophic ancestors allow for organic N sources to be used as well. Peptidase secretion is then used to reduce proteins from the soil into smaller peptide products. <ref name="foo" /> <br>


[[Image:Boletus_spp_UL_03.jpg|thumb|300px|left|<b<Figure 2:</b> Most species in the <i>Boletus</i> species of fungi exhibit ectomycorrhizal relationships with plants[https://www.first-nature.com/fungi/boletus-edulis.php].]]
[[Image:Boletus_spp_UL_03.jpg|thumb|300px|left|<b>Figure 2:</b> Most species in the <i>Boletus</i> species of fungi exhibit ectomycorrhizal relationships with plants[https://www.first-nature.com/fungi/boletus-edulis.php].]]


===Nitrogen and Carbon Transfer===
===Nitrogen and Carbon Transfer===
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After uptake to the fungal mycelium, nitrogen can be used in various ways by fungi. Some of the nitrogen is metabolized by the ECM fungi itself, while most is stored in cells or sent to fungal root tips to be transferred to a host plant. <ref>[https://doi.org/10.1111/nph.15257/ Nehls, Uwe, and Claude Plassard. "Nitrogen and phosphate metabolism in ectomycorrhizas." New Phytologist 220, no. 4 (2018): 1047-1058.]</ref> Once in the root tips, N has to cross two membranes to be imported to host cells. The process of nitrogen transfer across the plant-fungal interface requires a system of coordination in the expression of fungal and host N transporters, as well as aquaporins<ref>[https://doi.org/10.1111/j.1469-8137.2011.03651.x Dietz, Sandra, Julia von Bülow, Eric Beitz, and Uwe Nehls. "The aquaporin gene family of the ectomycorrhizal fungus Laccaria bicolor: lessons for symbiotic functions." New Phytologist 190, no. 4 (2011): 927-940.]</ref> and voltage-dependent cation channels.<ref>[https://doi.org/10.1016/j.tplants.2006.04.005 Chalot, Michel, Damien Blaudez, and Annick Brun. "Ammonia: a candidate for nitrogen transfer at the mycorrhizal interface." Trends in plant science 11, no. 6 (2006): 263-266..]</ref> <br><br>
After uptake to the fungal mycelium, nitrogen can be used in various ways by fungi. Some of the nitrogen is metabolized by the ECM fungi itself, while most is stored in cells or sent to fungal root tips to be transferred to a host plant. <ref>[https://doi.org/10.1111/nph.15257/ Nehls, Uwe, and Claude Plassard. "Nitrogen and phosphate metabolism in ectomycorrhizas." New Phytologist 220, no. 4 (2018): 1047-1058.]</ref> Once in the root tips, N has to cross two membranes to be imported to host cells. The process of nitrogen transfer across the plant-fungal interface requires a system of coordination in the expression of fungal and host N transporters, as well as aquaporins<ref>[https://doi.org/10.1111/j.1469-8137.2011.03651.x Dietz, Sandra, Julia von Bülow, Eric Beitz, and Uwe Nehls. "The aquaporin gene family of the ectomycorrhizal fungus Laccaria bicolor: lessons for symbiotic functions." New Phytologist 190, no. 4 (2011): 927-940.]</ref> and voltage-dependent cation channels.<ref>[https://doi.org/10.1016/j.tplants.2006.04.005 Chalot, Michel, Damien Blaudez, and Annick Brun. "Ammonia: a candidate for nitrogen transfer at the mycorrhizal interface." Trends in plant science 11, no. 6 (2006): 263-266..]</ref> <br><br>


Separately, hosts transport a third or more of their photosynthate to ECM fungi. <ref>[https://doi.org/10.1111/j.1438-8677.2009.00312.x Nehls, U., F. Göhringer, S. Wittulsky, and S. Dietz. "Fungal carbohydrate support in the ectomycorrhizal symbiosis: a review." Plant Biology 12, no. 2 (2010): 292-301.]</ref> This carbon is transferred in the form of sugars into the apoplastic space between plant and fungal cells.<ref>[https://doi.org/10.1111/ppl.12751 Hennion, Nils, Mickael Durand, Cécile Vriet, Joan Doidy, Laurence Maurousset, Rémi Lemoine, and Nathalie Pourtau. "Sugars en route to the roots. Transport, metabolism and storage within plant roots and towards microorganisms of the rhizosphere." Physiologia plantarum 165, no. 1 (2019): 44-57.
Separately, hosts transport a third or more of their photosynthate to ECM fungi. <ref>[https://doi.org/10.1111/j.1438-8677.2009.00312.x Nehls, U., F. Göhringer, S. Wittulsky, and S. Dietz. "Fungal carbohydrate support in the ectomycorrhizal symbiosis: a review." Plant Biology 12, no. 2 (2010): 292-301.]</ref> This carbon is transferred in the form of sugars into the apoplastic space between plant and fungal cells.<ref>[https://doi.org/10.1111/ppl.12751/ Hennion, Nils, Mickael Durand, Cécile Vriet, Joan Doidy, Laurence Maurousset, Rémi Lemoine, and Nathalie Pourtau. "Sugars en route to the roots. Transport, metabolism and storage within plant roots and towards microorganisms of the rhizosphere." Physiologia plantarum 165, no. 1 (2019): 44-57.]</ref> In order to execute this, plants encode sucrose transporters for long-distance transport within their own cells <ref>[https://doi.org/10.1016/j.tplants.2012.03.009 Doidy, Joan, Emily Grace, Christina Kühn, Françoise Simon-Plas, Leonardo Casieri, and Daniel Wipf. "Sugar transporters in plants and in their interactions with fungi." Trends in plant science 17, no. 7 (2012): 413-422.]</ref> and transfer sucrose cleavage products using monosaccharide transporters (SWEET transporters).<ref>[https://www.nature.com/articles/nature09606 Chen, Li-Qing, Bi-Huei Hou, Sylvie Lalonde, Hitomi Takanaga, Mara L. Hartung, Xiao-Qing Qu, Woei-Jiun Guo et al. "Sugar transporters for intercellular exchange and nutrition of pathogens." Nature 468, no. 7323 (2010): 527-532.
]</ref> In order to execute this, plants encode sucrose transporters for long-distance transport within their own cells <ref>[https://doi.org/10.1016/j.tplants.2012.03.009 Doidy, Joan, Emily Grace, Christina Kühn, Françoise Simon-Plas, Leonardo Casieri, and Daniel Wipf. "Sugar transporters in plants and in their interactions with fungi." Trends in plant science 17, no. 7 (2012): 413-422.
]</ref> and transfer sucrose cleavage products using monosaccharide transporters (SWEET transporters).<ref>[https://www.nature.com/articles/nature09606 Chen, Li-Qing, Bi-Huei Hou, Sylvie Lalonde, Hitomi Takanaga, Mara L. Hartung, Xiao-Qing Qu, Woei-Jiun Guo et al. "Sugar transporters for intercellular exchange and nutrition of pathogens." Nature 468, no. 7323 (2010): 527-532.
]</ref> While ECM fungi do express monosaccharide transporters, sucrose has been found to be an invalid nutrient as they lack expression of sucrose transporters and invertases. This means ECM fungi rely on their hosts to cleave photosynthate into usable monosaccharides. <ref>[https://www.nature.com/articles/nature06556 Martin, Francis, Andrea Aerts, Dag Ahrén, Aurélie Brun, E. G. J. Danchin, F. Duchaussoy, Julien Gibon et al. "The genome of Laccaria bicolor provides insights into mycorrhizal symbiosis." Nature 452, no. 7183 (2008): 88-92.
]</ref> While ECM fungi do express monosaccharide transporters, sucrose has been found to be an invalid nutrient as they lack expression of sucrose transporters and invertases. This means ECM fungi rely on their hosts to cleave photosynthate into usable monosaccharides. <ref>[https://www.nature.com/articles/nature06556 Martin, Francis, Andrea Aerts, Dag Ahrén, Aurélie Brun, E. G. J. Danchin, F. Duchaussoy, Julien Gibon et al. "The genome of Laccaria bicolor provides insights into mycorrhizal symbiosis." Nature 452, no. 7183 (2008): 88-92.
]</ref> <br>
]</ref> <br>

Revision as of 21:48, 7 December 2021

Introduction

An ectomycorrhiza is a mutualistic relationship occurring between fungi and the root systems of certain plants. Unlike other mycorrhizae, ectomycorrhizae aid their hosts by creating networks of hyphae surrounding roots. These networks mediate the exchange of nutrients to plants and carbon to fungi.
[1]

Figure 1: Hartig Nets are grown by ectomycorrhizal fungal to form the site of nutrient exchange. In arbuscular mycorrhiza, arbuscules penetrate cortical root cells to allow the exchange of phosphorus, carbon, and water.[1].

Nutritional Exchange

Uptake of Nitrogen

Ectomycorrhizal (ECM) fungi can uptake and provide a host with a wide range of macronutrients such as potassium, phosphorus, sulfur, and micronutrients such as iron, zinc, and copper. However, they are most recognized for the transport of nitrogen (N) as it is the main growth-limiting factor in many forest ecosystems. [2] The first step of nutritional exchange between ECM fungi and a plant host is for encoded N transporters to uptake and utilize nitrate and ammonium from the soil. The utilized N can be acquired from either inorganic or organic N sources. Ammonium can be taken up from inorganic sources and is the most preferred source by ECM fungi as it does not require energy to be used on chemical reduction. [3]

Three main ammonium transporters have been identified in several fungal ECM species: AMT1, AMT2, and AMT3. The former two are high-affinity transporters, meaning their expression is upregulated most in conditions of low ammonium. [4] Nitrate can also be uptaken by ECM fungi and requires the regulation of nitrate transporters, such as LbNRT2, and nitrate reductase enzymes. [5] In the presence of ammonium, the nitrate uptake pathway is downregulated due to the fungal preference for ammonium. The oxidative decomposition mechanisms inherited by ECM fungi from their saprotrophic ancestors allow for organic N sources to be used as well. Peptidase secretion is then used to reduce proteins from the soil into smaller peptide products. [3]

Figure 2: Most species in the Boletus species of fungi exhibit ectomycorrhizal relationships with plants[2].

Nitrogen and Carbon Transfer

After uptake to the fungal mycelium, nitrogen can be used in various ways by fungi. Some of the nitrogen is metabolized by the ECM fungi itself, while most is stored in cells or sent to fungal root tips to be transferred to a host plant. [6] Once in the root tips, N has to cross two membranes to be imported to host cells. The process of nitrogen transfer across the plant-fungal interface requires a system of coordination in the expression of fungal and host N transporters, as well as aquaporins[7] and voltage-dependent cation channels.[8]

Separately, hosts transport a third or more of their photosynthate to ECM fungi. [9] This carbon is transferred in the form of sugars into the apoplastic space between plant and fungal cells.[10] In order to execute this, plants encode sucrose transporters for long-distance transport within their own cells [11] and transfer sucrose cleavage products using monosaccharide transporters (SWEET transporters).[12] While ECM fungi do express monosaccharide transporters, sucrose has been found to be an invalid nutrient as they lack expression of sucrose transporters and invertases. This means ECM fungi rely on their hosts to cleave photosynthate into usable monosaccharides. [13]

Nutrient Quantity Regulation

A consensus on what moderates the carbon-nitrogen flux in ectomycorrhizae is not yet accepted, unlike carbon-phosphorus flux in arbuscular mycorrhizae.[14] One theory explaining flux regulation in ECM is the concept of “reciprocal rewards.” This proposes carbon and nitrogen transfer are one bidirectional system and that plants preferentially transfer more photosynthate to fungi that have provided the largest quantity of nutrients. Reciprocal rewards would allow for a more stable system of mutualism with selection for the fungi most efficient in nitrogen transfer.[15] Studies observing Pinus muriata-Suillus brevipes[16] and Fagus sylvatica associated fungi support this theory, demonstrating that nitrogen-enriched soil “hotspots” of ECM fungal mycelium are enriched with more carbon.[17]

However, other studies have results suggesting that N/C flux is neither reciprocal nor related. Pinus pinaster trees have been found to transfer C to their symbionts when it is excessively produced and continue that transfer even when the quantity of N received is lowered.[18] Also, when trees in N-limited boreal forests increase C allocation to fungi, they are not met with an increase in received N.[19] The mechanisms moderating C/N flux are still in dispute, but we know that under certain conditions C allocation may be decided by the N quantity transferred from ECM fungi.

Nitrogen Availability in Soil

Nitrogen depletion is known to be a main cause of growth limitation in many forest ecosystems. Some studies have shown that the addition of ECM fungi to forests can overcome nitrogen-driven growth limitations.[20] However, other evidence suggests that these fungi may enhance N limitation as they themselves utilize N in growth, and C allocation only heightens usage. This may promote ECM fungi to “hoard” N in forest ecosystems and further soil N limitation. [21] The persistence of ECM fungi may be partly explained by this limitation as an increased N concentration in soil leads to decreased species richness, plant colonization levels, mycelial growth, and sporocarp production.[22]

Genetics

Include some current research, with a second image.

Conclusion

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Include at least 5 references under References section.

References

  1. ↑ Tedersoo, L., May, T and Smith, M. "Ectomycorrhizal lifestyle in fungi: global diversity, distribution, and evolution of phylogenetic lineages" 2009. Mycorrhiza 20:217–263.
  2. ↑ Read, David J., Jonathan R. Leake, and Jesus Perez-Moreno. "Mycorrhizal fungi as drivers of ecosystem processes in heathland and boreal forest biomes." Canadian Journal of Botany 82, no. 8 (2004): 1243-1263.
  3. ↑ 3.0 3.1 Stuart, Emiko K., and Krista L. Plett. "Digging deeper: in search of the mechanisms of carbon and nitrogen exchange in ectomycorrhizal symbioses." Frontiers in plant science 10 (2020): 1658.
  4. ↑ Javelle, Arnaud, Mélanie Morel, Blanca‐Rosa Rodríguez‐Pastrana, Bernard Botton, Bruno André, Anne‐Marie Marini, Annick Brun, and Michel Chalot. "Molecular characterization, function and regulation of ammonium transporters (Amt) and ammonium‐metabolizing enzymes (GS, NADP‐GDH) in the ectomycorrhizal fungus Hebeloma cylindrosporum." Molecular microbiology 47, no. 2 (2003): 411-430.
  5. ↑ Kemppainen, Minna J., Maria C. Alvarez Crespo, and Alejandro G. Pardo. "fHANT‐AC genes of the ectomycorrhizal fungus Laccaria bicolor are not repressed by l‐glutamine allowing simultaneous utilization of nitrate and organic nitrogen sources." Environmental microbiology reports 2, no. 4 (2010): 541-553.
  6. ↑ Nehls, Uwe, and Claude Plassard. "Nitrogen and phosphate metabolism in ectomycorrhizas." New Phytologist 220, no. 4 (2018): 1047-1058.
  7. ↑ Dietz, Sandra, Julia von Bülow, Eric Beitz, and Uwe Nehls. "The aquaporin gene family of the ectomycorrhizal fungus Laccaria bicolor: lessons for symbiotic functions." New Phytologist 190, no. 4 (2011): 927-940.
  8. ↑ Chalot, Michel, Damien Blaudez, and Annick Brun. "Ammonia: a candidate for nitrogen transfer at the mycorrhizal interface." Trends in plant science 11, no. 6 (2006): 263-266..
  9. ↑ Nehls, U., F. Göhringer, S. Wittulsky, and S. Dietz. "Fungal carbohydrate support in the ectomycorrhizal symbiosis: a review." Plant Biology 12, no. 2 (2010): 292-301.
  10. ↑ Hennion, Nils, Mickael Durand, Cécile Vriet, Joan Doidy, Laurence Maurousset, Rémi Lemoine, and Nathalie Pourtau. "Sugars en route to the roots. Transport, metabolism and storage within plant roots and towards microorganisms of the rhizosphere." Physiologia plantarum 165, no. 1 (2019): 44-57.
  11. ↑ Doidy, Joan, Emily Grace, Christina Kühn, Françoise Simon-Plas, Leonardo Casieri, and Daniel Wipf. "Sugar transporters in plants and in their interactions with fungi." Trends in plant science 17, no. 7 (2012): 413-422.
  12. ↑ [https://www.nature.com/articles/nature09606 Chen, Li-Qing, Bi-Huei Hou, Sylvie Lalonde, Hitomi Takanaga, Mara L. Hartung, Xiao-Qing Qu, Woei-Jiun Guo et al. "Sugar transporters for intercellular exchange and nutrition of pathogens." Nature 468, no. 7323 (2010): 527-532. ]
  13. ↑ [https://www.nature.com/articles/nature06556 Martin, Francis, Andrea Aerts, Dag Ahrén, Aurélie Brun, E. G. J. Danchin, F. Duchaussoy, Julien Gibon et al. "The genome of Laccaria bicolor provides insights into mycorrhizal symbiosis." Nature 452, no. 7183 (2008): 88-92. ]
  14. ↑ [https://doi.org/10.1111/nph.13423 Garcia, Kevin, Pierre‐Marc Delaux, Kevin R. Cope, and Jean‐Michel Ané. "Molecular signals required for the establishment and maintenance of ectomycorrhizal symbioses." New Phytologist 208, no. 1 (2015): 79-87. ]
  15. ↑ Casieri, Leonardo, Nassima Ait Lahmidi, Joan Doidy, Claire Veneault-Fourrey, Aude Migeon, Laurent Bonneau, Pierre-Emmanuel Courty et al. "Biotrophic transportome in mutualistic plant–fungal interactions." Mycorrhiza 23, no. 8 (2013): 597-625.
  16. ↑ [https://link.springer.com/article/10.1007/s00572-018-00879-7 Bogar, Laura, Kabir Peay, Ari Kornfeld, Julia Huggins, Sara Hortal, Ian Anderson, and Peter Kennedy. "Plant-mediated partner discrimination in ectomycorrhizal mutualisms." Mycorrhiza 29, no. 2 (2019): 97-111. ]
  17. ↑ [https://ui.adsabs.harvard.edu/abs/2017EGUGA..1915133K/abstract Kaiser, Christina, Werner Mayerhofer, Marlies Dietrich, Stefan Gorka, Arno Schintlmeister, Siegfried Reipert, Peter Schweiger et al. "Reciprocal trade of Carbon and Nitrogen at the root-fungus interface in ectomycorrhizal beech plants." In EGU General Assembly Conference Abstracts, p. 15133. 2017. ]
  18. ↑ Bartlett et al.: Oncolytic viruses as therapeutic cancer vaccines. Molecular Cancer 2013 12:103.
  19. ↑ Corrêa, A., R. J. Strasser, and M. A. Martins-Loução. "Response of plants to ectomycorrhizae in N-limited conditions: which factors determine its variation? Mycorrhiza18: 413–427." (2008).
  20. ↑ Näsholm, Torgny, Peter Högberg, Oskar Franklin, Daniel Metcalfe, Sonja G. Keel, Catherine Campbell, Vaughan Hurry, Sune Linder, and Mona N. Högberg. "Are ectomycorrhizal fungi alleviating or aggravating nitrogen limitation of tree growth in boreal forests?." New Phytologist 198, no. 1 (2013): 214-221.
  21. ↑ Terrer, César, Sara Vicca, Bruce A. Hungate, Richard P. Phillips, and I. Colin Prentice. "Mycorrhizal association as a primary control of the CO2 fertilization effect." Science 353, no. 6294 (2016): 72-74.
  22. ↑ [0104:BEFCCO2.0.CO;2 Lilleskov, Erik A., Timothy J. Fahey, Thomas R. Horton, and Gary M. Lovett. "Belowground ectomycorrhizal fungal community change over a nitrogen deposition gradient in Alaska." Ecology 83, no. 1 (2002): 104-115.]


Edited by Ronan Daly, student of Joan Slonczewski for BIOL 116 Information in Living Systems, 2021, Kenyon College.

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