Activation of a Silent Fungal Polyketide Biosynthesis Pathway through Regulatory Cross Talk with a Cryptic Nonribosomal Peptide Synthetase Gene Cluster
Activation of a Silent Fungal Polyketide Biosynthesis Pathway through Regulatory Cross Talk with a Cryptic Nonribosomal Peptide Synthetase Gene Cluster
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DOI：
10.1128/aem.00683-10
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发表时间：
2010-12-01
影响因子：
4.4
通讯作者：
Brakhage, Axel A.
中科院分区：
文献类型：
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作者：
Bergmann, Sebastian;Funk, Alexander N.;Brakhage, Axel A.
丝状真菌产生许多天然产物，这些天然产物构成潜在药物先导物的一致来源，但似乎大多数天然产物被忽视，因为大多数生物合成基因簇在标准培养条件下是沉默的。筛选模式真菌构巢曲霉的次级代谢产物基因，我们注意到在染色体II上的沉默基因簇，包括两个非核糖体肽合成酶（NRPS）基因，inpA和inpB，侧翼的调控基因，我们命名为scpR的次级代谢交叉途径调节。使用醇脱氢酶AlcA的启动子诱导scpR基因的表达导致内源性scpR基因和NRPS基因的转录激活。令人惊讶的是，过表达scpR的菌丝体的上清液的代谢谱揭示了聚酮Asperfuranone的产生。通过转录组分析，我们发现另一个沉默的次级代谢产物基因簇位于染色体VIII上的编码曲霉呋喃酮的生物合成被特异性诱导。定量逆转录-PCR证明在alcAp-scpR诱导条件下，不仅相应的聚酮合成酶（PKS）合成基因afoE和afoG被转录，而且其激活因子afoA也被转录。为了排除inp簇的产物诱导曲霉呋喃酮基因簇的可能性，产生了携带NRPS基因inpB缺失以及alcAp-scpR过表达盒的菌株。在该菌株中，在诱导条件下，检测到含有NRPS的基因簇inp和除基因inpB外的曲霉呋喃酮基因簇的生物合成基因的转录本。此外，聚酮产物曲霉呋喃酮的存在表明转录因子ScpR控制曲霉呋喃酮生物合成基因簇的表达。这种表达以及曲霉呋喃酮的生物合成被废除后，曲霉呋喃酮激活基因afoA的删除，表明ScpR结合afoA启动子。据我们所知，这是第一次报告的两个生物合成基因簇位于不同的染色体之间的调控串扰。
Filamentous fungi produce numerous natural products that constitute a consistent source of potential drug leads, yet it seems that the majority of natural products are overlooked since most biosynthesis gene clusters are silent under standard cultivation conditions. Screening secondary metabolite genes of the model fungus Aspergillus nidulans, we noted a silent gene cluster on chromosome II comprising two nonribosomal peptide synthetase (NRPS) genes, inpA and inpB, flanked by a regulatory gene that we named scpR for secondary metabolism cross-pathway regulator. The induced expression of the scpR gene using the promoter of the alcohol dehydrogenase AlcA led to the transcriptional activation of both the endogenous scpR gene and the NRPS genes. Surprisingly, metabolic profiling of the supernatant of mycelia overexpressing scpR revealed the production of the polyketide asperfuranone. Through transcriptome analysis we found that another silent secondary metabolite gene cluster located on chromosome VIII coding for asperfuranone biosynthesis was specifically induced. Quantitative reverse transcription-PCR proved the transcription not only of the corresponding polyketide synthase (PKS) biosynthesis genes, afoE and afoG, but also of their activator, afoA, under alcAp-scpR-inducing conditions. To exclude the possibility that the product of the inp cluster induced the asperfuranone gene cluster, a strain carrying a deletion of the NRPS gene inpB and, in addition, the alcAp-scpR overexpression cassette was generated. In this strain, under inducing conditions, transcripts of the biosynthesis genes of both the NRPS-containing gene cluster inp and the asperfuranone gene cluster except gene inpB were detected. Moreover, the existence of the polyketide product asperfuranone indicates that the transcription factor ScpR controls the expression of the asperfuranone biosynthesis gene cluster. This expression as well as the biosynthesis of asperfuranone was abolished after the deletion of the asperfuranone activator gene afoA, indicating that ScpR binds to the afoA promoter. To the best of our knowledge, this is the first report of regulatory cross talk between two biosynthesis gene clusters located on different chromosomes.