Over-expression of the cercosporin facilitator protein, CFP, in Cercosporakikuchii up-regulates production and secretion of cercosporin

CFP (cercosporin facilitator protein), a light-regulated gene from the soyb ean fungal pathogen Cercospora kikuchii, encodes the putative major facilit ator transporter of the fungal polyketide cercosporin. Gene disruption of C FP in C kikuchii strain Gus-3 resulted in dramatically reduced cercosporin production and virulence, and increased sensitivity to the toxin. Two C kik uchii transformant strains (10-1 and 10-11) that over-produce cercosporin w ere recovered from the complementation of CFP gene-disrupted strain Gus-3. Southern analysis revealed that these strains contained multiple genomic co pies of CFP and over-expressed CFP transcript and protein. Although 10-1 an d 10-11 produce and secrete significantly elevated levels of cercosporin, t hey exhibit wild-type resistance to cercosporin, and maintain a wild-type p attern of light-regulated toxin accumulation. Restoration of wild-type cerc osporin resistance in 10-1 and 10-11 suggests that CFP does contribute subs tantially to cercosporin resistance via toxin secretion. The three-fold inc rease in toxin accumulation, predominately associated with the mycelium fra ction of these CFP multi-copy strains, suggests that CFP may also have a si gnificant, but unknown, role in regulating toxin production. (C) 2001 Feder ation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.