Analyse der RNA-Akkumulierung von Glomus intraradices zur Untersuchung der Funktion und der Entwicklung der arbuskulären Mykorrhiza

Arbuscular mycorrhizal fungi are obligate biotrophic organisms and form mutualistic interactions with more than 80% of plant species. Little is known about the molecular basics of the biotrophic status. In order to obtain details about the regulatory mechanisms, a suppressive subtractive hybridization cDNA-library was constructed. Only two fungal gene fragments could be isolated out of the intraradical mycelium of Glomus intraradices, putatively encoding a heatshock protein and a glyocal oxidase. In parallel established cDNA-libraries of genes from germinating spores and extraradical mycelium were extended with new sequences e.g. coding for proteins of the cytoskeleton, for transcription factors or transporters. The arbuscular mycorrhizal symbiosis is characterized by the bi-directional exchange of nutrients. The fungus supplies e.g. phosphate to the plant. One of the isolated gene fragments encodes for a regulatory protein of the phosphate uptake. This gene (GiPTaP) shows similar expression pattern as the already known phosphate transporter (GiPT). In return the plant delivers carbon to the fungus. Gene expression analysis of carbohydrate metabolic enzymes confirmed and supplemented previous physiological studies. RNA accumulation pattern in root organ and pot cultures indicates complex regulatory mechanisms for the fungal metabolism. Besides nutrient supply arbuscular mycorrhizal fungi also improve the plant resistance against heavy metals. Genes of glutathione transferases were isolated and expression studies indicate the role of this gene family in this bioprotection.