Inactivation of a cytochrome P-450 is a determinant of trichothecene diversity i

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Inactivation of a cytochrome P-450 is a determinant of trichothecene

diversity in Fusarium species*1

Daren W. Brown, , P. McCormick, J. , H.

Proctor and Anne E. Desjardins

Mycotoxin Research Unit, USDA/ARS, National Center for Agricultural

Utilization Research, 1815 N. University St., Peoria, IL 61604, USA

Received 28 November 2001; accepted 12 March 2002. Available

online 22 July 2002.

Abstract

Species of the genus Fusarium produce a great diversity of

agriculturally important trichothecene toxins that differ from each

other in their pattern of oxygenation and esterification. T-2 toxin,

produced by Fusarium sporotrichioides, and nivalenol (NIV), produced

by some strains of F. graminearum, contain an oxygen at the C-4

position. Deoxynivalenol (DON), produced by other strains of F.

graminearum, lacks a C-4 oxygen. NIV and DON are identical except

for this difference, whereas T-2 differs from these trichothecenes

at three other carbon positions. Sequence and Northern analyses of

the F. sporotrichioides genomic region upstream of the previously

described core trichothecene gene cluster have extended the cluster

by two genes: TRI13 and TRI14. TRI13 shares significant similarity

with the cytochrome P-450 class of enzymes, but TRI14 does not share

similarity with any previously characterized proteins. Gene

disruption and fermentation studies in F. sporotrichioides indicate

that TRI13 is required for the addition of the C-4 oxygen of T-2

toxin, but that TRI14 is not required for trichothecene

biosynthesis. PCR and sequence analyses indicate that the TRI13

homolog is functional in NIV-producing strains of F. graminearum but

nonfunctional in DON-producing strains of the fungus. These genetic

observations are consistent with chemical observations that

biosynthesis of T-2 toxin and NIV requires a C-4 hydroxylase while

biosynthesis of DON does not.

Author Keywords: Pathogenic fungi; Fusarium; P-450; Secondary

metabolism; Trichothecene gene cluster

*1 Sequence data from this paper have been deposited with the

GenBank Data Library under Accession Nos. AF359360, AF359361,

AY057841, AY057842, AY057843, and AY057844.

Corresponding author. Fax: +309-681-6689; email: browndw@....

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