Characterization of a Rice Protoplast-disrupting Factor Secreted by Rice Blast Fungus (Pyricularia oryzae Cav.)

Abstract

A concentrated culture filtrate of the rice blast fungus, Pyricularia oryzae, showed strong activity to disrupt protoplasts of rice leaves. The proportion of disrupted protoplasts decreased linearly with the logarithm of the dilution. The protoplast-disrupting factor was labile above 60°C, and was precipitated with 10% TCA (Trichloroacetic acid) or 50% saturated ammonium sulfate solution, suggesting its proteinaceous character. The factor was also precipitated with 80% acetone or ethanol. It was adsorbed to a DEAE-Toyopearl column, and then eluted with NaCl at about 0.1M. Via gel filtration on Sephacryl S-300, the factor was eluted as a major protein peak of approximately 30kDa. The fungal culture filtrate also disrupted protoplasts of wheat and rye but not those from barley or the three dicotyledonous plants, suggesting some host species specificity. Protoplast-disrupting activity of the culture filtrate appeared to be slightly higher in the incompatible combinations of rice cultivar and race of blast fungus than in the compatible combinations. The role of this factor in hypersensitive cell death at the early stage of infection is discussed.