title: Involvement of calcium/calmodulin signaling in cercosporin toxin biosynthesis by Cercospora nicotianae.
abstract: Cercosporin is a non-host-selective, perylenequinone toxin produced by many phytopathogenic Cercospora species. The involvement of Ca(2+)/calmodulin (CaM) signaling in cercosporin biosynthesis was investigated by using pharmacological inhibitors. The results suggest that maintaining endogenous Ca(2+) homeostasis is required for cercosporin biosynthesis in Cercospora nicotianae. The addition of excess Ca(2+) to the medium slightly increased fungal growth but resulted in a reduction in cercosporin production. The addition of Ca(2+) chelators [EGTA and 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid] also reduced cercosporin production. Ca(2+) channel blockers exhibited a strong inhibition of cercosporin production only at higher concentrations (>2 mM). Cercosporin production was reduced greatly by Ca(2+) ionophores (A23187 and ionomycin) and internal Ca(2+) blocker [3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester]. Phospholipase C inhibitors (lithium, U73122, and neomycin) led to a concentration-dependent inhibition of cercosporin biosynthesis. Furthermore, the addition of CaM inhibitors (compound 48/80, trifluoperazine, W-7, and chlorpromazine) also markedly reduced cercosporin production. In contrast to W-7, W-5, with less specificity for CaM, led to only minor inhibition of cercosporin production. The inhibitory effects of Ca(2+)/CaM inhibitors were partially or completely reversed by the addition of external Ca(2+). As assessed with Fluo-3/AM (a fluorescent Ca(2+) indicator), the Ca(2+) content in the cytoplasm decreased significantly when fungal cultures were grown in a medium containing Ca(2+)/CaM antagonists, confirming the specificity of those Ca(2+)/CaM antagonists in C. nicotianae. Taken together, the results suggest that Ca(2+)/CaM signal transduction may play a pivotal role in cercosporin biosynthesis in C. nicotianae.
authors.affiliation: Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, Florida 33850, USA. krchung@lal.ufl.edu
authors.forename: Kuang-Ren
authors.initials: KR
authors.lastname: Chung
mesh_terms: D001203:Ascomycota / Q000254:growth & development* / Q000378:metabolism; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003470:Culture Media; D015966:Gene Expression Regulation, Fungal; D007476:Ionophores / Q000494:pharmacology; D010569:Perylene / Q000031:analogs & derivatives* / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D002147:Calmodulin; D003470:Culture Media; D007476:Ionophores; D010716:Phosphatidylinositols; D010569:Perylene; C026363:cercosporin; D002118:Calcium