Identification of in planta-expressed arbuscular mycorrhizal fungal proteins upon comparison of the root proteomes of Medicago truncatula colonised with two Glomus species

In the absence of sequenced genomes for arbuscular mycorrhizal (AM) fungi, their obligatory biotrophy makes their intra-radical biology especially recalcitrant to functional analyses. Because tandem mass spectrometry-based proteomics enables fungal gene product identifications in phyla lacking genomic information, we have compared as a way to enlarge the coverage of in planta expressed-mycorrhiza-related proteins, the root proteome responses of Medicago truncatula upon colonisation with two AM fungi, Glomus mosseae and G. intraradices, using two-dimensional electrophoresis. In contrast to phosphate fertilization, mycorrhization led to specific changes in the abundance of 99 spots, including 42 overlapping modifications between G. mosseae- and G. intraradices-colonised roots. The 32 confident identifications that could be retrieved following tandem mass spectrometry encompassed 21 fungal proteins whose homology-inferred functions were found to complement the working models so far proposed for the intra-radical functioning of AM fungi with regard to carbon utilization, energy generation, redox homeostasis and protein turnover-related processes.