EXPRESSION OF A PATHOGENESIS-RELATED PEROXIDASE OF STYLOSANTHES HUMILIS IN TRANSGENIC TOBACCO AND CANOLA AND ITS EFFECT ON DISEASE DEVELOPMENT

In this study, we have investigated the effect of the expression of a cDNA (Shpx6a) encoding a pathogenesis-related peroxidase in the tropic al forage legume Stylosanthes humilis on fungal disease resistance in transgenic tobacco and canola plants. Constitutive expression of Shpx6 a cDNA was obtained using the 35S CaMV promoter in transgenic tobacco and canola plants and resulted in two to three fold increases in total peroxidase activity using guaiacol as a substrate. The peroxidase enc oded by Shpx6a was shown to be located in the apoplast. Inoculation ex periments using fungal pathogens Phytophthora parasitica var nicotiana e (black shank disease of tobacco) and Leptosphaeria maculans (blackle g disease of canola) showed that expression of Shpx6a peroxidase resul ted a small (20-30%) but statistically significant reduction in lesion development in the progeny of transgenic tobacco and canola lines. Th e enhanced level of tolerance to fungal diseases in both species appea rs to correlate with the level of peroxidase activity across several l ines of transgenic plants. These results provide evidence for a role f or the Shpx6a peroxidase in plant defence and suggest that it may be e mployed as a component of strategies aimed at the engineering of disea se resistance. (C) 1998 Elsevier Science Ireland Ltd. All rights reser ved.