VIEW ARTICLE

Biochemistry and Cell Biology

Evidence for Cutinase Production by Aspergillus flavus and Its Possible Role in Infection of Corn Kernels. B. Z. Guo, Department of Plant Pathology and Crop Physiology, Louisiana State University Agricultural Center, Baton Rouge, 70803; J. S. Russin(2), T. E. Cleveland(3), R. L. Brown(4), and K. E. Damann(5). (2)(5)Department of Plant Pathology and Crop Physiology, Louisiana State University Agricultural Center, Baton Rouge, 70803; (3)(4)U.S. Department of Agriculture, Agricultural Research Service, Southern Regional Research Center, New Orleans 70179. Phytopathology 86:824-829. Accepted for publication 25 April 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-824.

Aspergillus flavus can infect nondamaged corn kernels and produce aflatoxins before harvest. Experiments were conducted to determine if A. flavus produces cutinase and, if so, to investigate its possible role in kernel infection. Plate assays in vitro showed that A. flavus can grow on purified cutin as the sole carbon source and that it secretes extracellular cutinase. A. flavus grew better in liquid culture at pH 8 than at pH 6. Most cutinase substrate (p-nitrophenyl butyrate [PNB]) hydrolysis activity was in the 30% ammonium sulfate fraction. Two proteins with different PNB hydrolysis activity, designated C₁ and C₂, were isolated from A. flavus culture filtrates using native polyacrylamide gel electrophoresis. C₂ had greater PNB hydrolysis activity than C₁. The molecular weights for C₁ and C₂ were 36 kDa and 22 to 23 kDa, respectively. Kernels pretreated with bacterial cutinase or the 30% ammonium sulfate fraction from A. flavus culture filtrate supported increased levels of aflatoxin production similar to those in wounded kernels. The cutinase activity was strongly inhibited by diisopropyl fluorophosphate (DFP), a specific inhibitor of fungal cutinase, which indicated that A. flavus cutinase may be a serine esterase. Adding DFP to the spore suspension reduced aflatoxin production in kernels of Pioneer 3154 (susceptible) but not kernels of GT-MAS:gk (resistant). These data demonstrate that A. flavus secretes extracellular cutinase when growing on cutin-containing medium and suggest a possible role for cutinase in pathogenicity of A. flavus.