Molecular Physiology of Mycorrhiza

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Heads: Dieter Strack & Michael H. Walter

In the rhizosphere of natural ecosystems most herbaceous plants enter into a symbiotic relationship with a small number of fungal species to improve the acquisition of water and mineral nutrients from the soil. This interaction is called „Arbuscular Mycorrhiza“ (AM) – a term which originates from the haustoria-like fungal arbuscules, which are formed in the inner root cortex of such a „fungus root“. Arbuscules are the most important functional organs for nutrient exchange between the two partners of the AM symbiosis (Figure 1). The topics of the research group are mainly focused on alterations in plant isoprenoid metabolism induced by the interaction. Several fungus-stimulated gene activation events from the biosynthetic pathway of certain apocarotenoids, which accumulate to high concentrations in an AM-specific manner, have been characterized. Unravelling the importance of these apocarotenoids for the AM symbiosis is a major goal in the group. Furthermore, the regulation, evolution and role of the biosynthetic steps investigated in secondary (natural product) isoprenoid metabolism altogether are being examined.

Figure 1:

Scheme of mycorrhiza-mediated nutrient exchange in roots. Hyphae of arbuscular mycorrhizal fungi pervade the soil and collect nutrients, particularly phosphate (P), passing them down to the plant. Nutrient uptake from the fungus to the plant root occurs through arbuscules, which develop as highly ramified tiny „trees“ in the cells of the inner root cortex. Form there nutrients can further be transferred to the shoot. As a trade-off in the mutualistic symbiosis the fungus receives carbohydrates (C) from the plant.