Expression of a pathogenesis-related peroxidase of Stylosanthes humilis in transgenic tobacco and canola and its effect on disease development

Abstract

In this study, we have investigated the effect of the expression of a cDNA (Shpx6a) encoding a pathogenesis-related peroxidase in the tropical forage legume Stylosanthes humilis on fungal disease resistance in transgenic tobacco and canola plants. Constitutive expression of Shpx6a 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 encoded by Shpx6a was shown to be located in the apoplast. Inoculation experiments using fungal pathogens Phytophthora parasitica var nicotianae (black shank disease of tobacco) and Leptosphaeria maculans (blackleg disease of canola) showed that expression of Shpx6a peroxidase resulted a small (20–30%) but statistically significant reduction in lesion development in the progeny of transgenic tobacco and canola lines. The enhanced level of tolerance to fungal diseases in both species appears to correlate with the level of peroxidase activity across several lines of transgenic plants. These results provide evidence for a role for the Shpx6a peroxidase in plant defence and suggest that it may be employed as a component of strategies aimed at the engineering of disease resistance.