Increased trehalose biosynthesis in Hartig net hyphae of ectomycorrhizas

• Published in: The New phytologist Vol. 174; no. 2; pp. 389 - 398
• Main Authors: López, Mónica Fajardo, Männer, Philipp, Willmann, Anita, Hampp, Rüdiger, Nehls, Uwe
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.01.2007; Blackwell Publishing; Blackwell Publishing Ltd
• Subjects: Amanita; Amanita - enzymology; Amanita - genetics; Amanita - metabolism; Amanita muscaria; Amino Acid Sequence; Biosynthesis; Carbohydrate Metabolism; Carbohydrates; ectomycorrhiza; ectomycorrhizae; Ectomycorrhizas; enzyme activity; Fungi; Gene Expression; Glucosyltransferases - genetics; Glucosyltransferases - metabolism; Hyphae; Hyphae - enzymology; Hyphae - metabolism; Mycelium; Mycorrhizae - enzymology; Mycorrhizae - metabolism; Mycorrhizas; Nitrogen; Nitrogen - metabolism; Phosphoric Monoester Hydrolases - genetics; Phosphoric Monoester Hydrolases - metabolism; Populus - microbiology; Populus - physiology; Populus tremula; Rapid Report; Sequence Analysis, DNA; Symbiosis; Symbiosis - physiology; trehalose; Trehalose - biosynthesis; Trehalose - metabolism; trehalose phosphorylase; trehalose-6-phosphate synthase; trehalose-6-phosphate-phosphatase
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2007.01983.x

To obtain photoassimilates in ectomycorrhizal symbiosis, the fungus has to create a strong sink, for example, by conversion of plant-derived hexoses into fungus-specific compounds. Trehalose is present in large quantities in Amanita muscaria and may thus constitute an important carbon sink. In Amanita muscaria-poplar (Populus tremula x tremuloides) ectomycorrhizas, the transcript abundances of genes encoding key enzymes of fungal trehalose biosynthesis, namely trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP) and trehalose phosphorylase (TP), were increased. When mycorrhizas were separated into mantle and Hartig net, TPS, TPP and TP expression was specifically enhanced in Hartig net hyphae. Compared with the extraradical mycelium, TPS and TPP expression was only slightly increased in the fungal sheath, while the increase in the expression of TP was more pronounced. TPS enzyme activity was also elevated in Hartig net hyphae, displaying a direct correlation between transcript abundance and turnover rate. In accordance with enhanced gene expression and TPS activity, trehalose content was 2.7 times higher in the Hartig net. The enhanced trehalose biosynthesis at the plant-fungus interface indicates that trehalose is a relevant carbohydrate sink in symbiosis. As sugar and nitrogen supply affected gene expression only slightly, the strongly increased expression of the investigated genes in mycorrhizas is presumably developmentally regulated.