Towards the elucidation of AM-specific transcription in Medicago truncatula.

Roots of most plants form a mutualistic interaction with arbuscular mycorrhiza (AM) fungi. During the symbiosis, drastic morphological and physiological changes occur in the host plant root system. These changes are likely to be controlled by a specific genetic program of the plant. The legume Medicago truncatula is a model system widely used to elucidate this program. A number of loci required for AM-development have been identified by the analysis of M. truncatula mutants; however, the genes identified are also required for the Legume-Rhizobium symbiosis, since all M. truncatula mycorrhizal mutants so far reported are also nodulation mutants. We have focused on the identification and analysis of AM-specific genes as a further means to gain insight into the molecular background of the AM symbiosis and the molecular regulation of this tight symbiosis. Here, we describe the identification of AM-specific genes and the analysis of their transcriptional regulation. The identification of promoters and regulatory elements mediating the mycorrhiza-specific transcription provides a starting point to identify the corresponding specific transcription factors. This enables the identification of further upstream elements of the regulation cascade, and thus the elucidation of the molecular mechanisms controlling the AM-development within plant roots.