Isolation of a Potato Acidic 39 kDa β-1,3-glucanase with Antifungal Activity against Phytophthora infestans and Analysis of its Expression in Potato Cultivars Differing in their Degrees of Field Resistance

A β-1,3-glucanase (GLU-39) was isolated from a potato cultivar with a high level of field resistance (Solanum tuberosum L. cv Huinkul), after 72 h of infection with Phytophthora infestans when β-1,3-glucanase activity was markedly increased. Purification was performed by anion exchange chromatography, gel filtration and by chromatofocusing. A size of 39 kDa was estimated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis in denaturing conditions and by gel filtration, indicating the monomeric nature of GLU-39. The enzyme produces a direct inhibitory effect on the germination of sporangia of P. infestans. Differential expression (determined by immunoblotting assays) of GLU-39 was observed between two potato cultivars with different degrees of field resistance to P. infestans. In the resistant cultivar (cv Pampeana INTA) GLU-39 induction (four-fold with respect to healthy tubers) occurred 14 h after inoculation and remained over basal levels at 38 h after inoculation. By contrast, in the susceptible cultivar (cv Bintje), GLU-39 was induced at lower levels than those observed in cv Pampeana INTA, and no differences were detected between wounding and infection. The localization, expression pattern and in vitro activity suggest that GLU-39 may have a major role in field resistance.