Elucidating the molecular basis of effector-triggered host susceptibility mediated by the TAL-like effector Brg11 from the bacterial pathogen Ralstonia solanacearum

阐明细菌病原体青枯菌中 TAL 样效应子 Brg11 介导的效应子触发宿主易感性的分子基础

• 批准号: 413908990
• 负责人: Professor Dr. Thomas Lahaye
• 金额: --
• 依托单位: Abteilung für Allgemeine Genetik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/413908990?language=en
• 关键词: Elucidating; molecular; basis; effector; triggered

Plant pathogens pose a permanent thread to global food security. To invade plants, phytopathogenic microbes rely on effector proteins that they inject into host cells to promote host susceptibility. Knowledge of effector targets inside host cells provides a possibility for knowledge-based breeding of pest-resistant crops. Thus, elucidation of the molecular basis of effector-triggered host susceptibility remains a major aim of fundamental and applied plant pathology.We study Ralstonia solanacearum a devastating bacterial pathogen that triggers bacterial wilt disease on numerous crop species. We have characterized Brg11, a R. solanacearum effector with high similarity to transcription activator-like effectors (TALEs) from the bacterial genus Xanthomonas. TALEs bind to effector binding elements (EBEs) present in host promoters and transcriptionally activate downstream host susceptibility (S) genes to promote disease. Given its relatedness to TALEs it’s conceivable that Brg11 promotes disease by transcriptional activation of host S genes. Thus, we aimed to identify host genes that are transcriptionally activated by Brg11 to clarify how it promotes disease.To identify Brg11 host target genes we determined a preferred target sequence of Brg11 (Brg11-EBE). A 18bp-motif resembling Brg11-EBE was identified upstream of all arginine decarboxylase (ADC) genes in R. solanacearum host genomes and accordingly this motif was designated as ADC-box. Combined analysis of RNA-Seq data and target site prediction suggests that ADC1 and ADC2 are the only direct target genes of Brg11 in tomato. Inspection of Brg11-induced versus intrinsic ADC transcripts revealed short (100 bps) and long (450 bps) 5’UTRs, respectively. Preliminary data suggest that differences in their 5’UTRs cause that translation of intrinsic but not Brg11-induced transcripts is feedback regulated by metabolites that accumulate due to activity of ADC enzymes. Thus, Brg11-induced ADC transcripts likely evade translational control mechanisms that limit translation from intrinsic transcripts. In summary, our findings suggest that R. solanacearum Brg11 promotes bacterial wilt disease by transcriptional activation of host ADC genes.In the framework of this proposal we aim to:- study translational regulation of intrinsic versus Brg11-induced ADC transcripts- establish a catalogue of metabolites that change as consequence of elevated ADC protein levels- Analyze growth-inhibiting/promoting activity of Brg11-induced metabolites on plant associated microbes- Establish cellular reporters to visualize Brg11 target cells and Brg11-induced changes- Investigate Brg11-induced changes at the transcriptional and translational levelIn summary, these studies shall provide insights into how Brg11-induced activation of ADC genes promotes bacterial wilt disease.

植物病原体对全球粮食安全构成永久威胁。为了入侵植物，植物病原微生物依赖于它们注入宿主细胞中的效应蛋白来提高宿主的易感性。对宿主细胞内效应子靶标的了解为基于知识的抗虫作物育种提供了可能性。因此，阐明效应子触发的宿主易感性的分子基础仍然是基础和应用植物病理学的一个主要目标。我们研究了青枯雷尔斯顿菌（Ralstonia solanacearum），一种毁灭性的细菌病原体，可引发多种作物物种的青枯病。我们对 Brg11 进行了表征，它是一种青枯菌效应子，与黄单胞菌属的转录激活子样效应子 (TALE) 高度相似。 TALE 与宿主启动子中存在的效应结合元件 (EBE) 结合，并转录激活下游宿主易感性 (S) 基因以促进疾病。鉴于其与 TALE 的相关性，可以想象 Brg11 通过宿主 S 基因的转录激活来促进疾病。因此，我们的目的是鉴定由 Brg11 转录激活的宿主基因，以阐明它如何促进疾病。为了鉴定 Brg11 宿主靶基因，我们确定了 Brg11 的首选靶序列 (Brg11-EBE)。在青枯菌宿主基因组中所有精氨酸脱羧酶（ADC）基因的上游发现了一个类似于 Brg11-EBE 的 18bp 基序，因此该基序被命名为 ADC-box。 RNA-Seq数据和靶位点预测的结合分析表明，ADC1和ADC2是番茄中Brg11的唯一直接靶基因。对 Brg11 诱导的 ADC 转录本与内在 ADC 转录本的检查分别显示短 (100 bps) 和长 (450 bps) 5’UTR。初步数据表明，它们 5'UTR 的差异导致内在转录本的翻译而非 Brg11 诱导的转录本的翻译受到因 ADC 酶活性而积累的代谢物的反馈调节。因此，Brg11 诱导的 ADC 转录本可能会逃避限制内在转录本翻译的翻译控制机制。总之，我们的研究结果表明，青枯菌 Brg11 通过宿主 ADC 基因的转录激活促进青枯病。在本提案的框架内，我们的目标是：- 研究内在与 Brg11 诱导的 ADC 转录本的翻译调节- 建立因 ADC 蛋白水平升高而变化的代谢物目录- 分析 Brg11 诱导的生长抑制/促进活性 植物相关微生物的代谢物 - 建立细胞报告基因以可视化 Brg11 靶细胞和 Brg11 诱导的变化 - 在转录和翻译水平研究 Brg11 诱导的变化 总之，这些研究将为 Brg11 诱导的 ADC 基因激活如何促进青枯病提供见解。