Liaimer Anton, Helfrich Eric J N, Hinrichs Katrin, Guljamow Arthur, Ishida Keishi, Hertweck Christian, Dittmann Elke
Faculty of Biosciences, Fisheries and Economics, Department of Arctic and Marine Biology, Molecular Environments Group, University of Tromsø, 9037 Tromsø, Norway;
Leibniz Institute for Natural Product Research and Infection Biology, Hans Knöll Institute, 07745 Jena, Germany; and.
Proc Natl Acad Sci U S A. 2015 Feb 10;112(6):1862-7. doi: 10.1073/pnas.1419543112. Epub 2015 Jan 26.
Nostoc punctiforme is a versatile cyanobacterium that can live either independently or in symbiosis with plants from distinct taxa. Chemical cues from plants and N. punctiforme were shown to stimulate or repress, respectively, the differentiation of infectious motile filaments known as hormogonia. We have used a polyketide synthase mutant that accumulates an elevated amount of hormogonia as a tool to understand the effect of secondary metabolites on cellular differentiation of N. punctiforme. Applying MALDI imaging to illustrate the reprogramming of the secondary metabolome, nostopeptolides were identified as the predominant difference in the pks2(-) mutant secretome. Subsequent differentiation assays and visualization of cell-type-specific expression of nostopeptolides via a transcriptional reporter strain provided evidence for a multifaceted role of nostopeptolides, either as an autogenic hormogonium-repressing factor or as a chemoattractant, depending on its extracellular concentration. Although nostopeptolide is constitutively expressed in the free-living state, secreted levels dynamically change before, during, and after the hormogonium differentiation phase. The metabolite was found to be strictly down-regulated in symbiosis with Gunnera manicata and Blasia pusilla, whereas other metabolites are up-regulated, as demonstrated via MALDI imaging, suggesting plants modulate the fine-balanced cross-talk network of secondary metabolites within N. punctiforme.
点形念珠藻是一种多功能蓝细菌，它既可以独立生存，也可以与不同分类群的植物共生。研究表明，来自植物和点形念珠藻的化学信号分别刺激或抑制称为藻殖段的感染性运动丝状体的分化。我们使用了一种聚酮合酶突变体，该突变体积累了大量藻殖段，以此作为工具来了解次生代谢产物对点形念珠藻细胞分化的影响。通过基质辅助激光解吸电离成像（MALDI成像）来说明次生代谢组的重编程，结果确定诺斯托肽类化合物是pks2（-）突变体分泌组中的主要差异物质。随后的分化试验以及通过转录报告菌株对诺斯托肽类化合物的细胞类型特异性表达进行可视化，为诺斯托肽类化合物的多方面作用提供了证据，即根据其细胞外浓度，它既可以作为一种自身藻殖段抑制因子，也可以作为一种化学引诱剂。尽管诺斯托肽类化合物在自由生活状态下是组成型表达的，但在藻殖段分化阶段之前、期间和之后，其分泌水平会动态变化。通过MALDI成像证明，与大叶藻和短管藓共生时，该代谢产物被严格下调，而其他代谢产物则上调，这表明植物调节了点形念珠藻内次生代谢产物的精细平衡的相互作用网络。
