Departments of Medical Microbiology and Immunology Plant Pathology Genetics Bacteriology, University of Wisconsin-Madison, WI, USA.
Mol Microbiol. 2012 Mar;83(5):1024-34. doi: 10.1111/j.1365-2958.2012.07986.x. Epub 2012 Feb 10.
The eukaryotic bZIP transcription factors are critical players in organismal response to environmental challenges. In fungi, the production of secondary metabolites (SMs) is hypothesized as one of the responses to environmental insults, e.g. attack by fungivorous insects, yet little data to support this hypothesis exists. Here we establish a mechanism of bZIP regulation of SMs through RsmA, a recently discovered YAP-like bZIP protein. RsmA greatly increases SM production by binding to two sites in the Aspergillus nidulans AflR promoter region, a C6 transcription factor known for activating production of the carcinogenic and anti-predation SM, sterigmatocystin. Deletion of aflR in an overexpression rsmA (OE:rsmA) background not only eliminates sterigmatocystin production but also significantly reduces asperthecin synthesis. Furthermore, the fungivore, Folsomia candida, exhibited a distinct preference for feeding on wild type rather than an OE:rsmA strain. RsmA may thus have a critical function in mediating direct chemical resistance against predation. Taken together, these results suggest RsmA represents a bZIP pathway hardwired for defensive SM production.
真核生物 bZIP 转录因子是生物体应对环境挑战的关键参与者。在真菌中，次级代谢产物 (SMs) 的产生被假设为对环境胁迫的一种反应，例如食真菌昆虫的攻击，但支持这一假设的数据很少。在这里，我们通过最近发现的 YAP 样 bZIP 蛋白 RsmA 建立了 bZIP 调节 SMs 的机制。RsmA 通过与 Aspergillus nidulans AflR 启动子区域的两个位点结合，极大地增加了 SM 的产生，AflR 是一种已知的 C6 转录因子，可激活致癌和抗捕食 SM 麦角甾酮的产生。在过表达 rsmA (OE:rsmA) 背景下敲除 aflR 不仅消除了麦角甾酮的产生，而且还显著降低了asperthecin 的合成。此外，食真菌动物 Folsomia candida 明显更喜欢以野生型而不是 OE:rsmA 菌株为食。因此，RsmA 可能在介导对捕食的直接化学抗性方面具有关键功能。总之，这些结果表明 RsmA 代表了一种用于防御性 SM 产生的 bZIP 途径。
