Molecular analysis of the cercosporin biosynthetic gene cluster in Cercospora nicotianae

Abstract

We describe a core gene cluster, comprised of eight genes (designated CTB1-8), and associated with cercosporin toxin production in Cercospora nicotianae. Sequence analysis identified 10 putative open reading frames (ORFs) flanking the previously characterized CTB1 and CTB3 genes that encode, respectively, the polyketide synthase and a dual methyltransferase/monooxygenase required for cercosporin production. Expression of eight of the genes was co-ordinately induced under cercosporin-producing conditions and was regulated by the Zn(II)Cys(6) transcriptional activator, CTB8. Expression of the genes, affected by nitrogen and carbon sources and pH, was also controlled by another transcription activator, CRG1, previously shown to regulate cercosporin production and resistance. Disruption of the CTB2 gene encoding a methyltransferase or the CTB8 gene yielded mutants that were completely defective in cercosporin production and inhibitory expression of the other CTB cluster genes. Similar 'feedback' transcriptional inhibition was observed when the CTB1, or CTB3 but not CTB4 gene was inactivated. Expression of four ORFs located on the two distal ends of the cluster did not correlate with cercosporin biosynthesis and did not show regulation by CTB8, suggesting that the biosynthetic cluster was limited to CTB1-8. A biosynthetic pathway and a regulatory network leading to cercosporin formation are proposed.

Classification, Prediction, and Verification of the Regioselectivity of Fungal Polyketide Synthase Product Template Domains

“…The well-studied PksA and other NRPKSs that are involved in the synthesis of C4-C9/C2-C11 cyclized aromatic polyketides are clearly separated into Group IV. This group contains other known aflatoxin synthases that are analogues of PksA (45,46), as well as the heptaketide synthase cercosporin synthase CTB1 (47). Within this group, NRPKSs primed with different starter units are clearly divergent in sequence, as illustrated by the phylogenetic distance between the acetate-primed CTB1 and the hexanoate-primed aflatoxin synthases.…”

Total Biosynthesis of Diterpene Aphidicolin, a Specific Inhibitor of DNA Polymerase α: Heterologous Expression of Four Biosynthetic Genes inAspergillus oryzae

“…The numbers of biosynthetic genes for fungal metabolites are in general frequently less than those of metabolites from actinomycetes. Numerous biosynthetic gene clusters of fungal metabolites have recently been identified, including terpenes (gibberellin (7 genes) 32) ), peptides (terrequinone (5 genes) 35) and verruculogen (8 genes) 36) ), reduced polyketides (lovastatin (6 genes) 37) and solanapyrone (4 genes) 8) ), an aromatic polyketide (cercosporin (6 genes) 38) ), reduced-aromatic polyketide hybrids (radicicol (4 genes), 39) citrinin (4 genes) 40) and zearalenone (2 genes) 41) ), and a polyketide-peptide hybrid (chaetoglobosin (5-6 genes) 42) ). This observation indicates that the production of fungal bioactive natural products can be achieved by developing an efficient method for introducing multiple genes (less than 10) to such appropriate hosts as fungi and yeasts.…”

Quantitative phenotyping of grey leaf spot disease in maize using real-time PCR

“…One of the ESTs from which the CPR1_1 primers were designed (AF448828) was initially annotated as ctb4, one of the cercosporin biosynthesis genes (Shim and Dunkle 2002). However, this EST does not correspond to any of the three oxido-reductases of the well-characterized cercosporin biosynthetic cluster in Cercospora nicotianae (Chen et al 2007). This was supported by the fact that the second EST (FG242129) was cloned from C. zeaemaydis growing vegetatively, which are conditions when cercosporin biosynthesis is repressed (Bluhm et al 2008).…”