So far, no fusarin pathway-specific transcriptional factors have been identified,
but the impact of some global regulators on fusarin biosynthesis has been wellestablished [180]. The expression of the FUS genes is pH-dependent and is
upregulated in acidic conditions, but PacC TF is not involved in this process. FUS
expression is also nitrogen-dependent. The expression of the velvet-like complex
is increased in response to high nitrogen concentrations. Δvel1, Δvel2, and Δlae1
mutants produce significantly lower amounts of fusarins compared to the wild-type
strain. The deletion of a glutamine synthetase transcriptional factor gln1 dramatically
decreases FUS genes’ expression [182]. On the other hand, the epigenetic
modifications of histones like acetylation positively influence the expression of
FUS gene cluster [182].
5.1.7 Moniliformin
In 1973, Cole and co-workers have isolated a compound from F. moniliforme
cultures (later properly identified as F. proliferatum) which they called
moniliformin (MON) [191]. MON has a very simple chemical structure
(3-hydroxycyclobut-3-ene-1,2-dione) and is biosynthesized also by other Fusarium
species, e.g., F. avenaceum, F. oxysporum, F. fujikuroi, and F. subglutinans [192,
193]. This SM shows moderate toxicity toward plants and animals [144].
Moniliformin biosynthesis is a very short and simple process. Condensation of
two units of acetate leads to the formation of cyclobutadione moiety, which after
oxidation and dehydration results in MON synthesis [194]. Presumably due to the
uncomplicated biosynthetic pathway, until now all attempts to identify specific gene
cluster devoted to MON biosynthesis, as well as the pathway-specific regulators,
have failed.
5.2
Pigments
Fusaria produce a wide range of pigments, with the colors from pink, through
carmine red, to purple, but some species may also produce yellow and brown
pigments. Pigments can be best seen during the incubation of the fungus on rich
microbiological media on the plate reverse. Colors of fungal pigmentation depend on
the applied medium, its composition and pH.
Most of the Fusarium-produced pigments are naphthoquinones and javanicin,
anhydrojavanicin, fusarubin, anhydrofusarubin, bikaverin, bostricoidin, novarubin,
and naphthoquinone dimer – aurofusarin belong to this group. Many of these
compounds have antifungal and antibacterial properties which sometimes inhibit
the development of laboratory cell lines (e.g., HeLa). In this section we present the
most common Fusarium-produced pigments with known gene clusters: carotenoids,
bikaverin, and fusarubin [195].
5.2.1 Carotenoids
Carotenoids are characteristic yellow and orange pigments produced by plants,
algae, bacteria, and fungi including Fusaria. These pigments are tetraterpenoids
10 Fusarium Secondary Metabolism Biosynthetic Pathways: So Close but So. . .
229
but the impact of some global regulators on fusarin biosynthesis has been wellestablished [180]. The expression of the FUS genes is pH-dependent and is
upregulated in acidic conditions, but PacC TF is not involved in this process. FUS
expression is also nitrogen-dependent. The expression of the velvet-like complex
is increased in response to high nitrogen concentrations. Δvel1, Δvel2, and Δlae1
mutants produce significantly lower amounts of fusarins compared to the wild-type
strain. The deletion of a glutamine synthetase transcriptional factor gln1 dramatically
decreases FUS genes’ expression [182]. On the other hand, the epigenetic
modifications of histones like acetylation positively influence the expression of
FUS gene cluster [182].
5.1.7 Moniliformin
In 1973, Cole and co-workers have isolated a compound from F. moniliforme
cultures (later properly identified as F. proliferatum) which they called
moniliformin (MON) [191]. MON has a very simple chemical structure
(3-hydroxycyclobut-3-ene-1,2-dione) and is biosynthesized also by other Fusarium
species, e.g., F. avenaceum, F. oxysporum, F. fujikuroi, and F. subglutinans [192,
193]. This SM shows moderate toxicity toward plants and animals [144].
Moniliformin biosynthesis is a very short and simple process. Condensation of
two units of acetate leads to the formation of cyclobutadione moiety, which after
oxidation and dehydration results in MON synthesis [194]. Presumably due to the
uncomplicated biosynthetic pathway, until now all attempts to identify specific gene
cluster devoted to MON biosynthesis, as well as the pathway-specific regulators,
have failed.
5.2
Pigments
Fusaria produce a wide range of pigments, with the colors from pink, through
carmine red, to purple, but some species may also produce yellow and brown
pigments. Pigments can be best seen during the incubation of the fungus on rich
microbiological media on the plate reverse. Colors of fungal pigmentation depend on
the applied medium, its composition and pH.
Most of the Fusarium-produced pigments are naphthoquinones and javanicin,
anhydrojavanicin, fusarubin, anhydrofusarubin, bikaverin, bostricoidin, novarubin,
and naphthoquinone dimer – aurofusarin belong to this group. Many of these
compounds have antifungal and antibacterial properties which sometimes inhibit
the development of laboratory cell lines (e.g., HeLa). In this section we present the
most common Fusarium-produced pigments with known gene clusters: carotenoids,
bikaverin, and fusarubin [195].
5.2.1 Carotenoids
Carotenoids are characteristic yellow and orange pigments produced by plants,
algae, bacteria, and fungi including Fusaria. These pigments are tetraterpenoids
10 Fusarium Secondary Metabolism Biosynthetic Pathways: So Close but So. . .
229