Barad, S., Department of Postharvest Science of Fresh Produce, Volcani Center, Bet Dagan 50250, Israel, Department of Plant Pathology and Microbiology, Robert H. Smith Faculty of Agriculture,Food and Environment, Hebrew University of Jerusalem, Rehovot 76100, Israel
Horowitz, S.B., Department of Postharvest Science of Fresh Produce, Volcani Center, Bet Dagan 50250, Israel
Kobiler, I., Department of Postharvest Science of Fresh Produce, Volcani Center, Bet Dagan 50250, Israel
Sherman, A., Genomics Unit, ARO, Volcani Center, Israel
Prusky, D., Department of Postharvest Science of Fresh Produce, Volcani Center, Bet Dagan 50250, Israel

Penicillium expansum, the causal agent of blue mold rot, causes severe postharvest fruit maceration through secretion of D-gluconic acid (GLA) and secondary metabolites such as the mycotoxin patulin in colonized tissue. GLA involvement in pathogenicity has been suggested but the mechanism of patulin accumulation and its contribution to P. expansum pathogenicity remain unclear. The roles of GLA and patulin accumulation in P. expansum pathogenicity were studied using i) glucose oxidase GOX2-RNAi mutants exhibiting decreased GOX2 expression, GLA accumulation, and reduced pathogenicity; ii) IDH-RNAi mutants exhibiting downregulation of IDH (the last gene in patulin biosynthesis), reduced patulin accumulation, and no effect on GLA level; and iii) PACC-RNAi mutants exhibiting downregulation of both GOX2 and IDH that reduced GLA and patulin production. Present results indicate that conditions enhancing the decrease in GLA accumulation by GOX2- RNAi and PACC-RNAi mutants, and not low pH, affected patulin accumulation, suggesting GLA production as the driving force for further patulin accumulation. Thus, it is suggested that GLA accumulation may modulate patulin synthesis as a direct precursor under dynamic pH conditions modulating the activation of the transcription factor PACC and the consequent pathogenicity factors, which contribute to host-tissue colonization by P. expansum. © 2014 The American Phytopathological Society.