The transcription factor DksA exerts opposing effects on cell division depending on the presence of ppGpp.
The transcription factor DksA exerts opposing effects on cell division depending on the presence of ppGpp.
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细菌细胞大小是一种多因素性状，受营养可用性和细胞分裂时间等变量的影响。先前的工作揭示了大肠杆菌中alarmone（p）ppGpp（ppGpp）的浓度与细胞长度之间的负相关性，这表明ppGpp可能促进该生物体中分裂机构（分裂体）和胞质分裂的组装。为了阐明饥饿诱导的应激反应效应子和细胞增殖之间的这种违反直觉的联系，我们对大肠杆菌的生长和分裂进行了系统分析。在ppGpp合成中有缺陷的和/或被工程化以过量产生alarmone的大肠杆菌细胞。我们的数据表明，ppGpp间接作用于分裂体组装通过其作为一个全球性的转录介质的作用。ppGpp（ppGpp 0）或ppGpp相关转录因子DksA的缺失导致平均长度增加，ppGpp 0突变体也表现出极长丝状细胞的高频率。利用热敏分裂突变体和荧光标记的分裂蛋白，我们证实ppGpp和DksA是细胞分裂激活剂。我们发现，ppGpp和DksA调节分裂，通过其对转录的影响，虽然缺乏已知的分裂基因或监管机构在现有的转录组学数据强烈表明，这种调节是间接的。我们还发现，DksA抑制ppGpp 0细胞分裂，相反，它在野生型背景下的作用。我们提出ppGpp将DksA从分裂抑制剂转换为分裂激活剂的能力有助于在不同浓度的ppGpp中调节细胞长度。细胞分裂是细菌生命周期中的关键步骤，必须适当调节以确保存活。这项工作确定了alarmone（p）ppGpp（ppGpp）作为细胞分裂的一般调节因子，扩展了我们对ppGpp作用的理解，超越了饥饿和其他压力的信号。即使在营养充足的条件下，ppGpp的基础水平对于适当发生分裂和维持细胞大小至关重要。这项研究建立了ppGpp作为一个“开关”，控制转录因子DksA是否表现为分裂激活剂或抑制剂。这一意想不到的发现增强了我们对细菌所采用的复杂调控机制的理解，以协调细胞生长和应激反应的各个方面的分裂。由于分裂是一个必不可少的过程，因此更好地了解分裂机制的组装和激活机制可能有助于开发治疗细菌感染的新疗法。
Bacterial cell size is a multifactorial trait that is influenced by variables including nutritional availability and the timing of cell division. Prior work revealed a negative correlation between concentration of the alarmone (p)ppGpp (ppGpp) and cell length in Escherichia coli, suggesting that ppGpp may promote assembly of the division machinery (divisome) and cytokinesis in this organism. To clarify this counterintuitive connection between a starvation-induced stress response effector and cell proliferation, we undertook a systematic analysis of growth and division in E. coli cells defective in ppGpp synthesis and/or engineered to overproduce the alarmone. Our data indicate that ppGpp acts indirectly on divisome assembly through its role as a global mediator of transcription. Loss of either ppGpp (ppGpp0) or the ppGpp-associated transcription factor DksA led to increased average length, with ppGpp0 mutants also exhibiting a high frequency of extremely long filamentous cells. Using heat-sensitive division mutants and fluorescently labeled division proteins, we confirmed that ppGpp and DksA are cell division activators. We found that ppGpp and DksA regulate division through their effects on transcription, although the lack of known division genes or regulators in available transcriptomics data strongly suggests that this regulation is indirect. We also found that DksA inhibits division in ppGpp0 cells, contrary to its role in a wild-type background. We propose that the ability of ppGpp to switch DksA from a division inhibitor to a division activator helps tune cell length across different concentrations of ppGpp. Cell division is a key step in the bacterial lifecycle that must be appropriately regulated to ensure survival. This work identifies the alarmone (p)ppGpp (ppGpp) as a general regulator of cell division, extending our understanding of the role of ppGpp beyond a signal for starvation and other stress. Even in nutrient-replete conditions, basal levels of ppGpp are essential for division to occur appropriately and for cell size to be maintained. This study establishes ppGpp as a “switch” that controls whether the transcription factor DksA behaves as a division activator or inhibitor. This unexpected finding enhances our understanding of the complex regulatory mechanisms employed by bacteria to coordinate division with diverse aspects of cell growth and stress response. Because division is an essential process, a better understanding of the mechanisms governing the assembly and activation of the division machinery could contribute to the development of novel therapeutics to treat bacterial infections.
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