Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada.
Department of Biological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada.
PLoS One. 2020 Feb 28;15(2):e0226232. doi: 10.1371/journal.pone.0226232. eCollection 2020.
Pseudomonas chlororaphis strain PA23 is a biocontrol agent capable of protecting canola from stem rot disease caused by the fungal pathogen Sclerotinia sclerotiorum. PA23 produces several inhibitory compounds that are under control of a complex regulatory network. Included in this cascade is the PhzRI quorum sensing (QS) system, which plays an essential role in PA23 biocontrol, as well as CsaRI and AurRI, which have not yet been characterized in PA23. The focus of the current study was to employ RNA sequencing to explore the spectrum of PA23 genes under QS control. In this work, we investigated genes under the control of the main QS transcriptional regulator, PhzR, as well as those differentially expressed in an AHL-deficient strain, PA23-6863, which constitutively expresses an AiiA lactonase, rendering the strain QS defective. Transcriptomic profiling revealed 545 differentially expressed genes (365 downregulated; 180 upregulated) in the phzR mutant and 534 genes (382 downregulated; 152 upregulated) in the AHL-deficient PA23-6863. In both strains, decreased expression of phenazine, pyrrolnitrin, and exoprotease biosynthetic genes was observed. We have previously reported that QS activates expression of these genes and their encoded products. In addition, elevated siderophore and decreased chitinase gene expression was observed in the QS-deficient stains, which was confirmed by phenotypic analysis. Inspection of the promoter regions revealed the presence of "phz-box" sequences in only 58 of the 807 differentially expressed genes, suggesting that much of the QS regulon is indirectly regulated. Consistent with this notion, 41 transcriptional regulators displayed altered expression in one or both of the QS-deficient strains. Collectively, our findings indicate that QS governs expression of approximately 13% of the PA23 genome affecting diverse functions ranging from secondary metabolite production to general metabolism.
铜绿假单胞菌菌株 PA23 是一种生物防治剂，能够保护油菜免受真菌病原体核盘菌引起的茎腐病。PA23 产生几种受复杂调控网络控制的抑制性化合物。其中包括 PhzRI 群体感应 (QS) 系统，它在 PA23 的生物防治中起着至关重要的作用，以及 CsaRI 和 AurRI，它们在 PA23 中尚未被表征。本研究的重点是利用 RNA 测序来探索 QS 控制下 PA23 基因的谱。在这项工作中，我们研究了主要 QS 转录调节剂 PhzR 控制下的基因，以及在 AHL 缺陷菌株 PA23-6863 中差异表达的基因，该菌株组成型表达 AiiA 内酯酶，使菌株 QS 缺陷。转录组谱分析显示，phzR 突变体中有 545 个差异表达基因（365 个下调；180 个上调），AHL 缺陷的 PA23-6863 中有 534 个基因（382 个下调；152 个上调）。在这两种菌株中，观察到吩嗪、吡咯并[1,2-a]嘧啶和外蛋白酶生物合成基因的表达下调。我们之前报道过，QS 激活这些基因及其编码产物的表达。此外，在 QS 缺陷菌株中观察到铁载体基因表达上调和几丁质酶基因表达下调，这通过表型分析得到了证实。对启动子区域的检查表明，在 807 个差异表达基因中只有 58 个基因存在“phz-box”序列，这表明 QS 调控子的大部分是间接调控的。与这一观点一致，在一个或两个 QS 缺陷菌株中，有 41 个转录调节剂的表达发生了改变。总的来说，我们的研究结果表明，QS 控制着 PA23 基因组中约 13%的基因表达，影响从次生代谢产物生产到一般代谢等多种功能。
