EVIDENCE FOR THE REQUIREMENT OF EXTRACELLULAR PROTEASE IN THE PATHOGENIC INTERACTION OF PYRENOPEZIZA-BRASSICAE WITH OILSEED RAPE

Using a detached cotyledon test for pathogenicity, a UV-induced, non-pathogenic mutant of Pyrenopeziza brassicae was isolated which was also deficient in extracellular protease production in vitro. The proteolytic activity in the wild type was apparently due to a single cysteine protease with a mol. wt of 34 k, a temperature optimum of 40°C and a pH optimum of 8. When the mutant was crossed with a wild-type isolate of P. brassicae, the non-proteolytic and non-pathogenic traits co-segregated in the resulting progeny. The protease- mutant was transformed with clones from a genomic library of P. brassicae and a transformant obtained which had a single cosmid insert and showed concomitant restoration of pathogenicity and proteolytic activity in vitro. These results suggest that extracellular protease is a pathogenicity determinant of P. brassicae and possible functions for this protease in the disease process are discussed. © 1991 Academic Press Limited.