Fast track in vitro mycorrhization of potato plantlets allow studies on gene expression dynamics

Root colonization by arbuscular mycorrhizal (AM) fungi is a dynamic process involving major changes in plant gene expression. Here, the expression of a phosphate transporter gene (PT3) and several defense genes, already known to be involved in the various stages of AM establishment, were monitored in the mycelium donor plant (MDP) in vitro culture system associating potato plantlets with an AM fungus. This system allows fast and homogenous mycorrhization of seedlings at their early stage of development by growing the plantlets in active mycelial networks, but has never been validated for gene expression analysis. Here, QRT-PCR analyses were conducted in parallel to pre- (1 day), early (2 and 3 days), and late (6, 9, and 15 days) stages of root colonization. We observed the induction of a plant gene marker of AM root colonization (PT3) at the late stage and the induction of MAPK and PAL genes at the early and late stages of root colonization. We also demonstrated the induction of PR1 and PR2 genes at pre- and late stages and of GST1 and Lox genes at a late stage of root colonization. These results validated the MDP in vitro culture system as an optimal tool to study gene expression analysis during the AM fungi establishment. This system further opened the door to investigate gene networks associated with the plants-AM fungi symbiosis.