Fumonisins are linear, polyketide-derived molecules that can be classified as B or C fumonisins (FBs or FCs respectively) based on presence (FB) or absence (FC) of a terminal methyl group derived from an amino acid (Fig. Fumonisins are a family of mycotoxins that can accumulate in maize and some other crops (Munkvold and Desjardins, 1997 Moretti et al., 2010 Proctor et al., 2010), cause multiple diseases in animals, and are epidemiologically associated with esophageal cancer as well as neural tube defects in some human populations (Gelderblom et al., 1988 Marasas et al., 2004). The filamentous fungus Fusarium produces toxic secondary metabolites, also known as mycotoxins, that can accumulate in food and feed crops and thereby pose health risks to humans and livestock. Thus, uniform gene organization within the FUM cluster belies a complex evolutionary history that has not always paralleled the evolution of Fusarium.
Furthermore, low levels of FUM gene divergence in F. bulbicola, an FFSC species, and F. oxysporum provide evidence for horizontal transfer of the cluster from the former, or a closely related species, to the latter. The data are not consistent with balancing selection or interspecific hybridization, but they are consistent with two competing hypotheses: (i) multiple horizontal transfers of the cluster from unknown donors to FFSC recipients and (ii) cluster duplication and loss (birth and death). In addition, synonymous site divergence analyses indicated that three FUM cluster types predate diversification of FFSC. In FUM gene genealogies, evolutionary relationships between fusaria with different cluster types were largely incongruent with species relationships inferred from primary-metabolism (PM) gene genealogies, and FUM cluster types are not trans-specific.
Here, sequence analyses indicated that the cluster exists in five different genomic contexts, defining five cluster types. In Fusarium, fumonisin biosynthetic genes ( FUM) are clustered, and the cluster is uniform in gene organization. Fumonisins are a family of carcinogenic secondary metabolites produced by members of the Fusarium fujikuroi species complex (FFSC) and rare strains of Fusarium oxysporum.
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