Deletion of the adenylate cyclase (sac1) gene affects multiple developmental pathways and pathogenicity in Sclerotinia sclerotiorum

Sclerotinia sclerotiorum, a broad host range plant pathogen, produces pigmented, multihyphal sclerotia that are capable of long-term survival. Under favorable conditions, sclerotia carpogenically germinate to give rise to apothecia and forcibly discharged ascospores which serve as the primary source of inoculum in the disease cycle. The molecular regulator(S) of sclerotial development in filamentous fungi are largely unknown; however, pharmacological data has revealed that cyclic AMP (cAMP) negatively regulates sclerotial biogenesis in S. sclerotiorum. Based oil this observation, we analyzed the role of cAMP by deleting the single copy adenylatc cyclase (AC) sac1 gene from S. sclerotiorum. In Culture, cyclic AMP levels in the knock-out (KOI) strain were greatly reduced compared to wild type, the hyphal branching pattern was altered, microconidia (spermatia) were more abundant, and aberrant sclerotia were produced in a concentric pattern. The KO I strain was pathogenic oil mechanically wounded tissues however, virulence was severely attenuated. The pathogenicity defect on unwounded leaves is attributed to the absence of infection cushions and the attenuated virulence on wounded leaves correlates with the slow growth rate observed in Culture. This Study presents the first description of an adenylatc cyclase mutant that affects both pathogenicity and sclerotial development in a broad host range necrotroph. (c) 2006 Elsevier Inc. All rights reserved.