Upon
infection, phytopathogenic fungi secrete an array of hydrolytic
enzymes that can degrade components of the host epidermis, including
waxes, the cuticle, and cell walls.
Cellulases, which can hydrolyze crystalline
cellulose in the plant cell wall, are among these hydrolytic
enzymes. Here, we provide RNAi-based evidence to show that
cellulases belonging to glycosyl
hydrolase (GH) families 6 and 7 contribute to the penetration of the host epidermis and further invasion by the phytopathogenic fungus Magnaporthe oryzae. The GH6 and GH7
cellulases likely include all members of the
cellobiohydrolase family and some endoglucanases in M. oryzae. Quantitative
reverse-transcriptase polymerase chain reaction analysis indicated that more than half of the
cellulases were highly induced during
infection. We constructed knock-down (KD) mutants of these
cellulases using the building blocks method we reported previously. The transcript levels of the target genes and
cellulase activity were considerably reduced in the KD mutants. The KD mutants resulted in fewer lesions, less penetration, and
infection of fewer cells compared with the parent strain. Cytological analyses showed that a high rate of papilla formation blocked invasion of the KD mutants into host cells. These results suggest that the GH6 and GH7
cellulases play roles in the virulence of M. oryzae.