Antigenic glycoproteins in the teliospore wall of Tilletia indica

Abstract

We describe the partial characterization of immunoreactive glycoproteins in the teliospore wall of Tilletia indica, the causal agent of Karnal bunt of wheat (Triticum aestivum). Proteins from phenol-extracted and precipitated spore wall preparations were used as inject antigens to immunize New Zealand rabbits. Immunoblots of crude preparations of spore wall proteins probed with anti-T. indica spore wall IgG showed that the antibodies recognized a 37–43 kDa band present in the spore wall fraction of T. indica. A weakly immunoreactive band of the same mobility was detected in the spore wall of T. barclayana, a closely related fungal pathogen and causal agent of kernel smut of rice. The 37–43 kDa polypeptide could not be detected in the teliospore walls of the related fungal wheat pathogens T. controversa and T. tritici. Differential centrifugation of pulverized T. indica teliospores confirmed that the immunoreactive T. indica polypeptide was primarily localized in a 1500 g spore wall-enriched fraction and not in cytosolic or membrane fractions of the teliospores. The lectin concanavalin A bound to a 36–41 kDa polypeptide of T. indica but not T. barclayana. Treatment of spore wall proteins with glycosidase enzymes to remove oligosaccharide residues revealed that the 37–43 kDa polypeptide of T. indica was composed of two distinct immunoreactive polypeptides of lower molecular weight than those detected in undigested spore wall protein immunoblots. The immunoreactivity of the 37–43 kDa T. barclayana protein was lost upon enzymatic deglycosylation. This suggests the cross reactivity between the 37–43 kDa antigen of T. barclayana and T. indica is most likely due to oligosaccharide epitopes common to the glycoproteins. The differential reactivity of the deglycosylated proteins comprising the 37–43 kDa antigens provides a potential target for development of rapid immunological diagnostic assays for teliospores of different smut pathogens.