Molecular-physiological aspects of the AM symbiosis post penetration

Abstract

The establishment of an arbuscular mycorrhizal symbiosis is -characterised by several stages until the fungus has penetrated the root epidermis. The present chapter deals with the subsequent phase where the fungus colonises the root cortex and, when the different functions of the symbiosis are realised. After summarising the morphological and cytological characteristics of this symbiotic phase, different strategies will be described which have been followed to understand the molecular-physiological basis of the symbiosis. Non-targeted approaches resulted in new hypotheses concerning mycorrhizal functioning based on the identification of -differentially expressed transcripts or proteins. Some of these hypotheses were further proofed by various biological techniques as localisation of the gene products or down-regulation of the genes in transgenic plants. In contrast targeted approaches were directed to particular plant and fungal functions. Among those functions, the present chapter will concentrate on the assimilation, the metabolism and the distribution of carbohydrates in the plant and the fungus.