No abstract

The rice sheath blight pathogen, Rhizoctonia solani, produces a toxin designated as RS-toxin, a carbohydrate compound containing mainly alpha-glucose and mannose. Different microflora were tested for RS-toxin inactivation. Isolates of Trichoderma viride inactivated this toxin when it was provided as the sole food source, and these isolates reduced the severity of toxin-induced symptoms and electrolyte leakage from rice cells. The best-performing isolate, TvMNT7, produced two extracellular proteins of 110 and 17 kDa. The high molecular mass protein was shown to have alpha-glucosidase activity. The purified 110 kDa protein was able to reduce RS-toxin activity.

No abstract

Aims: To purify and characterize an extracellular a-glucosidase from Trichoderma viride capable of inactivating a host-speci®c phytotoxin, designated RS toxin, produced by the rice sheath blight pathogen, Rhizoctonia solani Ku Èhn. Methods and Results: The host-speci®c RS toxin was puri®ed from both culture ®ltrates (culture ®ltrate toxin, CFTox) and R. solani-inoculated rice sheaths (sheath blight toxin, SBTox). Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analyses of extracellular proteins, puri®ed from a biocontrol fungus T. viride (TvMNT7) grown on SBTox and CFTox separately, were carried out. The antifungal activity of the puri®ed high molecular weight protein (110 kDa) was studied against RS toxin as well as on the sclerotial germination and mycelial growth of R. solani. Enzyme assay and Western blot analysis with the antirabbit TvMNT7 110-kDa protein indicated that the protein was an a-glucosidase. The 110-kDa protein was highly speci®c to RS toxin and its Michaelis±Menten constant value was 0á40 mmol l )1 when p-nitrophenyl a-D D-glucopyranoside was used as the substrate. The isoelectric point of the protein was 5á2. N-terminal sequencing of the a-glucosidase protein showed that its amino acid sequence showed no homology with other known a-glucosidases.Conclusions: This appears to be the ®rst report of the puri®cation and characterization of an a-glucosidase capable of inactivating a host-speci®c toxin of fungal origin. The a-glucosidase is speci®c to RS toxin and is different from the known a-glucosidases. Signi®cance and Impact of the Study: As RS toxin could be inactivated by the microbial a-glucosidase enzyme, isolation of the gene that codes for the enzyme from T. viride and transfer of the gene to rice plants would lead to enhanced resistance against sheath blight pathogen by inactivation of RS toxin.

No abstract