Jiangsu Key Laboratory for Microbes and Functional Genomics, Jiangsu Engineering and Technology Research Center for Microbiology, College of Life Sciences, Nanjing Normal University, Nanjing, China.
Departments of Medicine and of Microbiology and Immunology, McGill University, Montréal, Canada.
mBio. 2020 Nov 10;11(6):e02329-20. doi: 10.1128/mBio.02329-20.
Polysaccharides are key components of both the fungal cell wall and biofilm matrix. Despite having distinct assembly and regulation pathways, matrix exopolysaccharide and cell wall polysaccharides share common substrates and intermediates in their biosynthetic pathways. It is not clear, however, if the biosynthetic pathways governing the production of these polysaccharides are cooperatively regulated. Here, we demonstrate that cell wall stress promotes production of the exopolysaccharide galactosaminogalactan (GAG)-depend biofilm formation in the major fungal pathogen of humans and that the transcription factor SomA plays a crucial role in mediating this process. A core set of SomA target genes were identified by transcriptome sequencing and chromatin immunoprecipitation coupled to sequencing (ChIP-Seq). We identified a novel SomA-binding site in the promoter regions of GAG biosynthetic genes and , as well as its regulators and Strikingly, this SomA-binding site was also found in the upstream regions of genes encoding the cell wall stress sensors, chitin synthases, and β-1,3-glucan synthase. Thus, SomA plays a direct regulation of both GAG and cell wall polysaccharide biosynthesis. Consistent with these findings, SomA is required for the maintenance of normal cell wall architecture and compositions in addition to its function in biofilm development. Moreover, SomA was found to globally regulate glucose uptake and utilization, as well as amino sugar and nucleotide sugar metabolism, which provides precursors for polysaccharide synthesis. Collectively, our work provides insight into fungal adaptive mechanisms in response to cell wall stress where biofilm formation and cell wall homeostasis were synchronously regulated. The cell wall is essential for fungal viability and is absent from human hosts; thus, drugs disrupting cell wall biosynthesis have gained more attention. Caspofungin is a member of a new class of clinically approved echinocandin drugs to treat invasive aspergillosis by blocking β-1,3-glucan synthase, thus damaging the fungal cell wall. Here, we demonstrate that caspofungin and other cell wall stressors can induce galactosaminogalactan (GAG)-dependent biofilm formation in the human pathogen We further identified SomA as a master transcription factor playing a dual role in both biofilm formation and cell wall homeostasis. SomA plays this dual role by direct binding to a conserved motif upstream of GAG biosynthetic genes and genes involved in cell wall stress sensors, chitin synthases, and β-1,3-glucan synthase. Collectively, these findings reveal a transcriptional control pathway that integrates biofilm formation and cell wall homeostasis and suggest SomA as an attractive target for antifungal drug development.
多糖是真菌细胞壁和生物膜基质的关键组成部分。尽管它们具有不同的组装和调控途径，但基质胞外多糖和细胞壁多糖在其生物合成途径中共享共同的底物和中间产物。然而，目前尚不清楚调控这些多糖产生的生物合成途径是否协同调控。在这里，我们证明细胞壁应激促进了人类主要真菌病原体中依赖半乳氨基半乳糖（GAG）的胞外多糖生物膜形成，转录因子 SomA 在介导这一过程中起着至关重要的作用。通过转录组测序和染色质免疫沉淀结合测序（ChIP-Seq），我们鉴定了一组核心的 SomA 靶基因。我们在 GAG 生物合成基因 和 的启动子区域以及其调控因子 和 中鉴定了一个新的 SomA 结合位点。值得注意的是，这个 SomA 结合位点也存在于编码细胞壁应激传感器、几丁质合酶和β-1,3-葡聚糖合酶的基因的上游区域。因此，SomA 直接调控 GAG 和细胞壁多糖的生物合成。与这些发现一致，SomA 除了在生物膜发育中的功能外，还需要维持正常的细胞壁结构和组成。此外，发现 SomA 全局调控葡萄糖摄取和利用以及氨基糖和核苷酸糖代谢，为多糖合成提供前体。总之，我们的工作提供了对真菌应对细胞壁应激的适应性机制的深入了解，其中生物膜形成和细胞壁动态平衡被同步调控。细胞壁对真菌的生存至关重要，而在人体宿主中不存在；因此，破坏细胞壁生物合成的药物受到了更多的关注。卡泊芬净是一类新型临床批准的棘白菌素类药物中的一种，通过阻断β-1,3-葡聚糖合酶来治疗侵袭性曲霉病，从而破坏真菌细胞壁。在这里，我们证明了卡泊芬净和其他细胞壁应激物可以诱导人类病原体中的半乳氨基半乳糖（GAG）依赖性生物膜形成。我们进一步鉴定了 SomA 作为一个主转录因子，在生物膜形成和细胞壁动态平衡中发挥双重作用。SomA 通过直接结合 GAG 生物合成基因和参与细胞壁应激传感器、几丁质合酶和β-1,3-葡聚糖合酶的基因上游保守的基序发挥双重作用。总之，这些发现揭示了一个整合生物膜形成和细胞壁动态平衡的转录控制途径，并表明 SomA 是抗真菌药物开发的一个有吸引力的靶点。
