Griffiths Scott, Saccomanno Benedetta, de Wit Pierre J G M, Collemare Jérôme
Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708PB Wageningen, The Netherlands.
Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708PB Wageningen, The Netherlands.
Fungal Genet Biol. 2015 Nov;84:52-61. doi: 10.1016/j.fgb.2015.09.009. Epub 2015 Sep 28.
Cladosporium fulvum is a non-obligate biotrophic fungal tomato pathogen for which fifteen secondary metabolite (SM) gene clusters were previously identified in its genome. However, most of these SM biosynthetic pathways remain cryptic during growth in planta and in different in vitro conditions. The sole SM produced in vitro is the pigment cladofulvin. In this study, we attempted to activate cryptic pathways in order to identify new compounds produced by C. fulvum. For this purpose, we manipulated orthologues of the global regulators VeA, LaeA and HdaA known to regulate SM biosynthesis in other fungal species. In C. fulvum, deleting or over-expressing these regulators yielded no new detectable SMs. Yet, quantification of cladofulvin revealed that CfHdaA is an activator whilst CfVeA and CfLaeA seemed to act as repressors of cladofulvin production. In the wild type strain, cladofulvin biosynthesis was affected by the carbon source, with highest production under carbon limitation and traces only in presence of saccharose. Repression of cladofulvin production by saccharose was dependent on both CfVeA and CfLaeA. Deletion of CfVeA or CfLaeA caused production of sterile mycelia, whilst Δcfhdaa deletion mutants sporulated, suggesting that cladofulvin production is not linked to asexual reproduction. Profiling the transcription of these regulators showed that CfHdaA-mediated regulation of cladofulvin production is independent of both CfVeA and CfLaeA. Our data suggest CfLaeA directly affects cladofulvin production whilst the effect of CfVeA is indirect, suggesting a role for CfLaeA outside of the Velvet complex. In conclusion, our results showed that regulation of SM production in C. fulvum is different from other fungi and indicate that manipulation of global regulators is not a universal tool to discover new fungal natural products.
番茄褐孢霉是一种非专性活体营养型真菌番茄病原菌，此前在其基因组中鉴定出了15个次生代谢产物（SM）基因簇。然而，这些SM生物合成途径中的大多数在植物体内生长以及不同体外条件下仍处于隐秘状态。体外产生的唯一SM是色素枝孢菌素。在本研究中,我们试图激活隐秘途径以鉴定番茄褐孢霉产生的新化合物。为此,我们操纵了已知在其他真菌物种中调节SM生物合成的全局调节因子VeA、LaeA和HdaA的直系同源物。在番茄褐孢霉中,删除或过表达这些调节因子均未产生新的可检测到的SM。然而,枝孢菌素的定量分析表明,CfHdaA是一种激活剂,而CfVeA和CfLaeA似乎是枝孢菌素产生的抑制剂。在野生型菌株中,枝孢菌素的生物合成受碳源影响,在碳限制条件下产量最高,而仅在蔗糖存在时产生微量。蔗糖对枝孢菌素产生的抑制依赖于CfVeA和CfLaeA。删除CfVeA或CfLaeA会导致产生不育菌丝体,而Δcfhdaa缺失突变体形成孢子,这表明枝孢菌素的产生与无性繁殖无关。对这些调节因子的转录进行分析表明,CfHdaA介导的枝孢菌素产生的调节独立于CfVeA和CfLaeA。我们的数据表明,CfLaeA直接影响枝孢菌素的产生,而CfVeA的作用是间接的,这表明CfLaeA在Velvet复合体之外发挥作用。总之,我们的结果表明番茄褐孢霉中SM产生的调节与其他真菌不同,并表明操纵全局调节因子不是发现新的真菌天然产物的通用工具。
