Article

Mastering ectomycorrhizal symbiosis: the impact of carbohydrates.

Universität Tübingen, Botanisches Institut, Physiologische Okologie der Pflanzen, Auf der Morgenstelle 1, D-72076 Tübingen, Germany.
Journal of Experimental Botany (impact factor: 5.36). 02/2008; 59(5):1097-108. DOI:10.1093/jxb/erm334 pp.1097-108
Source: PubMed

ABSTRACT Mycorrhiza formation is the consequence of a mutualistic interaction between certain soil fungi and plant roots that helps to overcome nutritional limitations faced by the respective partners. In symbiosis, fungi contribute to tree nutrition by means of mineral weathering and mobilization of nutrients from organic matter, and obtain plant-derived carbohydrates as a response. Support with easily degradable carbohydrates seems to be the driving force for fungi to undergo this type of interaction. As a consequence, the fungal hexose uptake capacity is strongly increased in Hartig net hyphae of the model fungi Amanita muscaria and Laccaria bicolor. Next to fast carbohydrate uptake and metabolism, storage carbohydrates are of special interest. In functional A. muscaria ectomycorrhizas, expression and activity of proteins involved in trehalose biosynthesis is mainly localized in hyphae of the Hartig net, indicating an important function of trehalose in generation of a strong carbon sink by fungal hyphae. In symbiosis, fungal partners receive up to approximately 19 times more carbohydrates from their hosts than normal leakage of the root system would cause, resulting in a strong carbohydrate demand of infected roots and, as a consequence, a more efficient plant photosynthesis. To avoid fungal parasitism, the plant seems to have developed mechanisms to control carbohydrate drain towards the fungal partner and link it to the fungus-derived mineral nutrition. In this contribution, current knowledge on fungal strategies to obtain carbohydrates from its host and plant strategies to enable, but also to control and restrict (under certain conditions), carbon transfer are summarized.

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Keywords

carbon transfer
 
certain conditions
 
control carbohydrate
 
current knowledge
 
degradable carbohydrates
 
driving force
 
fast carbohydrate uptake
 
fungal hyphae
 
fungal parasitism
 
fungus-derived mineral nutrition
 
Hartig net
 
Hartig net hyphae
 
mineral weathering
 
mutualistic interaction
 
plant roots
 
plant-derived carbohydrates
 
special interest
 
storage carbohydrates
 
tree nutrition
 
trehalose biosynthesis
 

Uwe Nehls