et al. (2011) demonstrated that polymorphisms of TRI8 resulted in the chemotype of
AcDON [98]. Moreover, in F. sporotrichioides, which is a T-2 toxin producer, the
biosynthesis pathway proceeds with the products FsTri1, FsTri16, and FsTri8 [89,
97]. In most F. graminearum strains, TRI1 is responsible for trichothecene oxygenation at both C-7 and C-8, which leads to the formation of variants like DON or
NIV [99]. Nevertheless, in some F. graminearum strains, TRI1 adds a hydroxyl
group at C-7 only, leading to the formation of the T-2 toxin [77].
5.1.2 Fumonisins
Fumonisins are a group of mycotoxins primarily produced by F. verticillioides,
F. fujikuroi, and F. proliferatum, worldwide pathogens of rice and maize but also
found on a wide range of other agro-food crops [4, 12, 60]. Other species from the
F. fujikuroi species complex also produce fumonisins, but they are of minor importance. Interestingly, there are also species that are fumonisin nonproducers, and for
some the status is ambiguous, as at least some strains were found to produce
fumonisins for F. oxysporum, F. temperatum, or F. subglutinans [4, 7, 8]. The
synthesis of FBs in association with disease symptoms differs markedly depending
on the host conditions and infected tissue type [100]. It has been shown that
fumonisins produced by F. verticillioides have a slight impact on maize ear rot
development and significant effect on maize seedling blight. The successful transformation of the fumonisin-producing genes into an endophytic, fumonisin-nonproducing F. verticillioides strain has converted this endophyte into a pathogen that
causes seedling blight disease in maize [101, 102], strongly supporting
the hypothesis that fumonisin is a pathogenicity factor during maize seedling
infection [102].
At least 28 different analogs of fumonisins were described and divided into four
main categories: A, B, C, and P series [103, 104]. The most important group are the
B fumonisins, B 1 , B 2 , B 3 , and B 4 , mainly due to their toxicity to humans and
animals. Fumonisin B 1 is also, apart from Aspergilli-produced aflatoxins, the most
abundant and important contaminant of maize and maize-derived products. The
structures of FBs were first described in 1988 and 1989 by the researchers in
South Africa, New Caledonia, and France [105, 106]. The B series fumonisins
have a 20-carbon polyketide backbone with terminal amine residue, several
hydroxyl groups, and two propane-1,2,3-tricarboxylate esters at various positions.
The A and P series fumonisins differ due to alteration or replacement of the terminal
amine group, while the C series fumonisins have a 19-carbon backbone [1, 2, 17].
Fumonisins that are characterized by an unsubstituted primary amino group at the
C-2, and structurally close to sphingolipids, actually can disturb the sphingolipid
metabolism by inhibiting the enzyme ceramide synthase and consequently lead to
the degeneration of the sphingolipid-rich tissues and disruption of cell membrane
integrity [107].
Fumonisin biosynthetic (FUM) gene cluster has been first described in
F. verticillioides belonging to the Fusarium fujikuroi species complex (FFSC),
containing 17 genes encoding biosynthetic enzymes, a transcription factor, and
an ABC transporter [4, 80, 103, 108]. The FUM1 gene encodes a polyketide
10 Fusarium Secondary Metabolism Biosynthetic Pathways: So Close but So. . .
221
AcDON [98]. Moreover, in F. sporotrichioides, which is a T-2 toxin producer, the
biosynthesis pathway proceeds with the products FsTri1, FsTri16, and FsTri8 [89,
97]. In most F. graminearum strains, TRI1 is responsible for trichothecene oxygenation at both C-7 and C-8, which leads to the formation of variants like DON or
NIV [99]. Nevertheless, in some F. graminearum strains, TRI1 adds a hydroxyl
group at C-7 only, leading to the formation of the T-2 toxin [77].
5.1.2 Fumonisins
Fumonisins are a group of mycotoxins primarily produced by F. verticillioides,
F. fujikuroi, and F. proliferatum, worldwide pathogens of rice and maize but also
found on a wide range of other agro-food crops [4, 12, 60]. Other species from the
F. fujikuroi species complex also produce fumonisins, but they are of minor importance. Interestingly, there are also species that are fumonisin nonproducers, and for
some the status is ambiguous, as at least some strains were found to produce
fumonisins for F. oxysporum, F. temperatum, or F. subglutinans [4, 7, 8]. The
synthesis of FBs in association with disease symptoms differs markedly depending
on the host conditions and infected tissue type [100]. It has been shown that
fumonisins produced by F. verticillioides have a slight impact on maize ear rot
development and significant effect on maize seedling blight. The successful transformation of the fumonisin-producing genes into an endophytic, fumonisin-nonproducing F. verticillioides strain has converted this endophyte into a pathogen that
causes seedling blight disease in maize [101, 102], strongly supporting
the hypothesis that fumonisin is a pathogenicity factor during maize seedling
infection [102].
At least 28 different analogs of fumonisins were described and divided into four
main categories: A, B, C, and P series [103, 104]. The most important group are the
B fumonisins, B 1 , B 2 , B 3 , and B 4 , mainly due to their toxicity to humans and
animals. Fumonisin B 1 is also, apart from Aspergilli-produced aflatoxins, the most
abundant and important contaminant of maize and maize-derived products. The
structures of FBs were first described in 1988 and 1989 by the researchers in
South Africa, New Caledonia, and France [105, 106]. The B series fumonisins
have a 20-carbon polyketide backbone with terminal amine residue, several
hydroxyl groups, and two propane-1,2,3-tricarboxylate esters at various positions.
The A and P series fumonisins differ due to alteration or replacement of the terminal
amine group, while the C series fumonisins have a 19-carbon backbone [1, 2, 17].
Fumonisins that are characterized by an unsubstituted primary amino group at the
C-2, and structurally close to sphingolipids, actually can disturb the sphingolipid
metabolism by inhibiting the enzyme ceramide synthase and consequently lead to
the degeneration of the sphingolipid-rich tissues and disruption of cell membrane
integrity [107].
Fumonisin biosynthetic (FUM) gene cluster has been first described in
F. verticillioides belonging to the Fusarium fujikuroi species complex (FFSC),
containing 17 genes encoding biosynthetic enzymes, a transcription factor, and
an ABC transporter [4, 80, 103, 108]. The FUM1 gene encodes a polyketide
10 Fusarium Secondary Metabolism Biosynthetic Pathways: So Close but So. . .
221