3b. Comparative analyses

Modification of the Medicago truncatula root proteome during the early stage of arbuscular mycorrhizal symbiosis was investigated by comparing, using two-dimensional electrophoresis, the protein patterns obtained from non-inoculated roots and roots synchronized for Glomus intraradices appressorium formation. This approach was conducted in wild-type (J5), mycorrhiza-defective (TRV25, dmi3) and autoregulation-defective (TR122, sunn) M. truncatula genotypes. The groups of proteins that responded to appressorium formation were further compared between wild-type and mutant genotypes: few overlaps and major differences were recorded demonstrating that mutations in DMI3 and SUNN modified the appressorium-responsive root proteome. Except a chalcone reductase, none of the differentially-displayed proteins that could be identified using MALDI-TOF mass spectrometry was previously known as appressorium responsive. A DMI3-dependent increased accumulation of signal transduction-related proteins (dehydroascorbate reductase, cyclophilin, actin depolymerisation factor) was found to precede mycorrhiza establishment. Differences in the accumulation of proteins related to plant defence reactions, cytoskeleton rearrangements and auxin signalling upon symbiont contact were recorded between wild-type and hyper-mycorrhizal genotypes, pointing to some putative pathways by which SUNN may regulate very early arbuscule formation.