SNF1 protein kinase is important for growth and full virulence of Botrytis cinerea.

At early stages of infection, Botrytis cinerea secretes a wide spectrum of plant cell wall degrading enzymes (CWDEs) to facilitate penetration into host. So far, only the polygalacturonases PG1 and PG2 and the xylanase XYN11A were proved by reverse genetics to be required for virulence. Verification of the function of single members of the different CWDE classes is indeed difficult, due to gene redundancy in multigenic families. In various plant pathogenic fungi, production of these enzymes is under catabolic repression and positively regulated by the snf1 (sucrose non-fermenting 1) gene which is expressed when glucose is depleted. To examine the function of the snf1 gene in B. cinerea, knock-out mutants were obtained by targeted mutagenesis. The growth of the Δsnf1 mutants was compared with the wild type strain on minimal medium enriched with different simple and complex carbon sources (fructose, sucrose, glucose, xylan, xylose, pectin, polygalacturonic acid, cellulose). A significant reduction of growth was observed on some carbon sources except with glucose and xylan. Microscopic studies verified, that the sporulation of the mutants was almost abolished and unusually shaped mycelia were found. Pathogenicity tests performed on apple fruits displayed a strong defect in colonization by the Δsnf1 mutants with a 60% decrease in virulence. Pathogenicity tests on plant systems are in progress together with the characterization of possible effects on secretion and expression of CWDEs.