López Mónica Fajardo, Männer Philipp, Willmann Anita, Hampp Rüdiger, Nehls Uwe
Eberhard Karls Universität, Physiologische Ökologie der Pflanzen, Auf der Morgenstelle 1, D-72076 Tübingen, Germany.
New Phytol. 2007;174(2):389-398. 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.
为了在菌根共生中获取光合产物，真菌必须建立一个强大的库，例如，通过将植物来源的己糖转化为真菌特异性化合物。在毒蝇鹅膏中大量存在海藻糖，因此它可能构成一个重要的碳库。在毒蝇鹅膏-杨树（欧洲山杨×美洲山杨）外生菌根中，编码真菌海藻糖生物合成关键酶的基因，即海藻糖-6-磷酸合酶（TPS）、海藻糖-6-磷酸磷酸酶（TPP）和海藻糖磷酸化酶（TP）的转录丰度增加。当菌根被分离为菌套和哈氏网时，TPS、TPP和TP的表达在哈氏网菌丝中特异性增强。与根外菌丝相比，TPS和TPP的表达在真菌鞘中仅略有增加，而TP表达的增加更为明显。TPS酶活性在哈氏网菌丝中也有所升高，显示出转录丰度与周转率之间的直接相关性。与增强的基因表达和TPS活性一致，哈氏网中海藻糖含量高出2.7倍。植物-真菌界面处海藻糖生物合成的增强表明海藻糖是共生中一个相关的碳水化合物库。由于糖和氮供应对基因表达的影响很小，菌根中所研究基因的强烈增加表达可能是受发育调控的。
