Defense responses related to mycorrhizal-induced resistance in wheat against Zymoseptoria tritici

• Root inoculation with F. mosseae protects wheat leaves against STB. • A systemic up-regulation of defense genes occurs in the leaves of mycorrhizal plants. • A similar set of defense genes is induced by the pathogen itself in leaves. • Blumenol derivatives are accumulated in mycorrhizal wheat plants. • Metabolite balance is slightly affected in the leaves of mycorrhizal wheat plants. Arbuscular mycorrhizal fungi (AMFs) are considered promising biocontrol agents that can provide protection to plants against bio-aggressors through the triggering of mycorrhiza-induced resistance (MIR). Here, the protective systemic effect of the AMF species Funneliformis mosseae was evaluated in a susceptible wheat cultivar against Septoria tritici blotch (STB), caused by the hemibiotrophic ascomycete Zymoseptoria tritici . Mycorrhizal inoculation led to a root colonization rate of 42 % in 50-day-old wheat plants, associated with an overexpression of genes encoding nutrient transporters in roots and the accumulation of blumenol derivatives in roots and leaves, attesting to a functional mycorrhizal symbiosis. Concomitantly, mycorrhizal wheat plants exhibited a foliar protection rate of 78 % against Z. tritic i. An up-regulation of two defense-related genes ( PR1 and POX ) in wheat leaves was also revealed consecutively to the AMF symbiosis establishment and prior to pathogen attack. These two genes and five other genes ( PR5 , PAL , GST , CalS , and CAD ) were also up-regulated in leaves infected by Z. tritici alone during its biotrophic stage, whereas six genes ( PR1 , PR4 , PR5 , PAL , POX , and CalS ) were up-regulated in mycorrhizal and Z. tritici -inoculated plants. Less accumulation of tryptophan and methylpipecolic acid was observed in infected leaves of mycorrhizal plants, indicating a stress alleviation in mycorrhizal wheat plants under Z. tritici attack. Our findings highlight the ability of F. mosseae to activate MIR and to protect wheat against Z. tritici by specifically remodeling gene expression in leaves.