Pyrrocidine, a molecular off switch for fumonisin biosynthesis
Fig 10
Illustration of biological antagonism between two maize seed endophytes, F. verticillioides and S. zeae.
F. verticillioides is primarily confined to the pedicel of the maize kernel, while S. zeae is more frequently isolated from embryonic tissue. Pyrrocidine A and B, two lactam-containing antibiotics produced by S. zeae, are postulated to contribute to an allelopathic antagonism between the two fungi. The chemical structures of pyrrocidines differ by a double (red circle) or single bond within lactam ring, resulting in higher toxicity of pyrrocidine A than B. Detailed analyses were carried out for an ABC transporter encoding gene, FvABC3, and a putative zinc-binding dehydrogenase encoding gene, FvZBD1. We hypothesize that FvABC3 facilitates persistence of F. verticillioides in maize seeds when encountering pyrrocidines, while the pyrrocidines induce the expression of FvZBD1 in F. verticillioides, a gene negatively impacting the production of fumonisins and virulence in maize seedlings. FvZBD1 is the most highly induced gene in both pyrrocidine A and B treatments, and its impact on fumonisin production provides evidence for allelochemical activity and response.