Benzoxazinoids as key factors in maize colonization and growth promotion by the endophytic fungus Colletotrichum tofieldiae

In recent decades, fungal endophytes have emerged as essential tools for enhancing plant productivity and resilience in a sustainable manner.However, the mechanisms underlying fungal endophyte colonization and their beneficial effects on plants remain poorly understood.Colletotrichum tofieldiae (Ct) is a fungal endophyte that promotes growth and improves yield of maize (Fig. 1, Daz-Gonzlez et al., 2020;Daz-Gonzlez et al. 2025).To investigate the genes and mechanisms involved in establishing this beneficial interaction, we analyzed RNA-seq data from Ct-inoculated maize seedlings at early post-inoculation stages (Figs. 2 and3).Our results have revealed a prominent role of maize secondary metabolite biosynthetic pathways associated with defense responses.While pathways for terpenoid phytoalexin are induced in Ct-inoculated plants, the biosynthetic route of benzoxazinoids (BXs) is notably repressed (Figs. 4 and5).A similar although stronger response is observed in plants inoculated with the phytopathogen C. graminearum (Fig. 6).BXs are indole-derived defense compounds unique to grasses, and are highly toxic to Ct (Fig. 7).We demonstrate that BXs repression enhances maize root colonization by Ct and increases Ct plant growth promotion (Figs. 8 and9).