Assessment of blast disease resistance in transgenic PRms rice using a gfp-expressing Magnaporthe oryzae strain

Rice blast caused by the fungus Magnaportbe oryzae (anamorph Pyricularia grisea) is one of the most devastating diseases Of Cultivated rice worldwide. In this study, a green fluorescent protein (gfp)-expressing M. oryzae strain was generated and used to investigate the infection process in a commercial rice cultivar. Expression of the gfp gene did not affect the pathogenicity of the M. oryzae transformants. Confocal microscopy allowed in vivo imaging of this pathogen during infection of rice tissues. Magnaportbe oryzae pathogenicity was examined on both leaf and root tissues. In roots of wild-type plants, the fungus penetrated into epidermal and cortical cells, and colonized the central cylinder and xylem vessels. However, the dimorphic growth pattern typically observed during the biotrophic and necrotrophic stages of leaf colonization was not observed during colonization of root tissues. Furthermore, events Occurring during infection of rice plants constitutively expressing the maize pathogenesis-related PRms gene were characterized and compared with those occurring during the interaction of this pathogen with untransformed rice plants. Fungal penetration was drastically reduced and delayed in tissues of PRms plants compared to untransformed plants. These results indicated that the gfp-expressing M. oryzae represents a strategic tool for the assessment of blast disease resistance in transgenic rice which can be also applied to the analysis of the M. oryzae interaction with other cultivars or mutants of important crop species.