Auxin Production by the Rice Blast Fungus and its Localization in Host Tissue

Abstract The rice blast fungus Magnaporthe oryzae requires living plant cells in its early stages of infection and invasion of host tissue. In this study, we showed the possibility that an exogenous fungal auxin could be implicated in hemibiotrophic interactions. Chemical analyses showed that this fungus produces a small amount of the auxin indole‐3‐acetic acid during growth in culture. Immunohistological analyses showed that antigens of the anti‐indole‐3‐acetic acid monoclonal antibody were localized in the fungal infection hyphae present in the rice tissue. Rice transformants containing an auxin‐inducible reporter construct demonstrated an auxin response around the apex of the infection hyphae after fungal invasion of living tissue. These results suggest that the rice blast fungus produces a small amount of auxin during its biotrophic phase and the invaded rice tissue responds to the exogenous fungal auxin. This auxin may be involved in the biotrophic phase of the infection hyphae.