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Applied and Environmental Microbiology, February 2003, p. 1187-1196, Vol. 69, No. 2
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.2.1187-1196.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Involvement of Calcium/Calmodulin Signaling in Cercosporin Toxin Biosynthesis by Cercospora nicotianae

Kuang-Ren Chung^1,2*

Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, Florida 33850,¹ Department of Plant Pathology, University of Florida, Gainesville, Florida 32611²

Received 12 June 2002/ Accepted 30 October 2002

Cercosporin is a non-host-selective, perylenequinone toxin produced by many phytopathogenic Cercospora species. The involvement of Ca²⁺/calmodulin (CaM) signaling in cercosporin biosynthesis was investigated by using pharmacological inhibitors. The results suggest that maintaining endogenous Ca²⁺ homeostasis is required for cercosporin biosynthesis in Cercospora nicotianae. The addition of excess Ca²⁺ to the medium slightly increased fungal growth but resulted in a reduction in cercosporin production. The addition of Ca²⁺ chelators [EGTA and 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid] also reduced cercosporin production. Ca²⁺ channel blockers exhibited a strong inhibition of cercosporin production only at higher concentrations (>2 mM). Cercosporin production was reduced greatly by Ca²⁺ ionophores (A23187 and ionomycin) and internal Ca²⁺ 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 Ca²⁺/CaM inhibitors were partially or completely reversed by the addition of external Ca²⁺. As assessed with Fluo-3/AM (a fluorescent Ca²⁺ indicator), the Ca²⁺ content in the cytoplasm decreased significantly when fungal cultures were grown in a medium containing Ca²⁺/CaM antagonists, confirming the specificity of those Ca²⁺/CaM antagonists in C. nicotianae. Taken together, the results suggest that Ca²⁺/CaM signal transduction may play a pivotal role in cercosporin biosynthesis in C. nicotianae.

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* Mailing address: University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Rd., Lake Alfred, FL 33850. Phone: (863) 956-1151, ext. 369. Fax: (863) 956-4631. E-mail: krchung{at}lal.ufl.edu.

Approved for publication as journal series no. R-08884 of the Florida Agricultural Experiment Station.

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Applied and Environmental Microbiology, February 2003, p. 1187-1196, Vol. 69, No. 2
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.2.1187-1196.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Chen, H.-Q., Lee, M.-H., Chung, K.-R. (2007). Functional characterization of three genes encoding putative oxidoreductases required for cercosporin toxin biosynthesis in the fungus Cercospora nicotianae. Microbiology 153: 2781-2790 [Abstract] [Full Text]