In natural ecosystems, the roots of most vascular plants exist in symbiotic association with arbuscular mycorrhizal (AM) fungi. These are mutually beneficial associations, in which the plants provides carbon to the fungus while the fungus assists the plant with the acquisition of phosphate and other mineral nutrients from the environment. To gain a better understanding at molecular level of the development, functioning and regulation of the AM symbiosis, a cDNA library was prepared from Medicago truncatula roots colonized with the arbuscular mycorrhizal fungus, Glomus versiforme . EST sequencing of the clones from the library has been conducted and 7351 ESTs from the library have been annotated by TIGR and deposited at NCBI. Preliminary clustering analyses performed by TIGR, indicates that 93 tentative contigs (TC) of ESTs are unique to the M. truncatula /G. versiforme library and 4421 tentative uni-genes were also identified in this library. The temporal expression profiles of 2228 uni-gene during development of the mycorrhiza have been conducted using macro-arrays. The arrays were hybridized with 33P labeled first-strand cDNA probes prepared from M. truncatula / G. versiforme roots and mock-inoculated M. truncatula roots. A set of genes showing significantly altered expression have been identified. Differential expression of a selection of these genes has also been confirmed on northern blots. The analysis of function and mycorrhizal specificity of selected genes has been initiated.

Key words: Glomus versiforme , Medicago truncatula, cDNA arrays, gene profiling, mycorrhizal