Analyse der Genregulation in Medicago truncatula und Pisum sativum während der Entwicklung arbuskulärer Mykorrhiza

Arbuscular mycorrhiza (AM) is a symbiotic interaction between plant roots and soil fungi of the phylum Glomeromycota, which leads to an improved nutrient supply to plants, primarily phosphate. Promoter activity of the proton-pumping ATPase Mtha1 was localised in arbuscle-containing cortex cells as well as in the fixation zone and meristeme of nodules in Medicago truncatula roots. The generated electrochemical gradient could be involved in nutrient transfer in mycorrhizal and in nodulated roots. A successful establishment of the AM is associated with a bidirectional signal exchange between both symbionts. Phytohormones regulate plant growth and development. Increased levels of the phytohormones, abscisic acid (ABA) and indole-3-butyric acid (IBA), in mycorrhizal roots could also support formation of symbiotic structures. Plant gene expression is therefore not only altered by AM fungi but also by secondary effects like changing levels of phytohormones and phosphate in mycorrhizal root tissue. Investigation of the root transcriptome of M. truncatula resulted in the identification of 568 genes, regulated by different AM fungi (Glomus mosseae, Glomus intraradices, Gigaspora rosea), but not by ABA, IBA or phosphate. Strong variation of plant gene expression emphasizes physiological and morphological differences in mycorrhizas, caused by different AM fungi. Application of suppressive subtractive hybridisation in combination with macroarray analysis resulted in the identification of 17 genes in Pisum sativum induced by mycorrhiza, but not by the symbiont Sinorhizobium meliloti or by the pathogen Aphanomyces euteiches. With one exception all genes showed an arbuscle-associated expression, which could be confirmed for nine candidates by Nothern blot analysis and semiquantitative RT-PCR respectively. By sequence comparison of P. sativum genes with EST databases of M. truncatula a trypsin inhibitor gene family was found also with transcript accumulation in mycorrhizal roots, confirmed by Real-Time-PCR. M. truncatula is therefore a useful model organism for better characterization of important crop plants like P. sativum.