Segregation of four Agrobacterium tumefaciens replicons during polar growth: PopZ and PodJ control segregation of essential replicons
Segregation of four Agrobacterium tumefaciens replicons during polar growth: PopZ and PodJ control segregation of essential replicons
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DOI：
10.1073/pnas.2014371117
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发表时间：
2020-10
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通讯作者：
J. S. Robalino-Espinosa;J. S. Robalino-Espinosa;John R. Zupan;A. Chávez-Arroyo;P. Zambryski
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作者：
J. S. Robalino-Espinosa;J. S. Robalino-Espinosa;John R. Zupan;A. Chávez-Arroyo;P. Zambryski
细菌无处不在，必不可少，而且种类繁多。许多传染性物种不遵循模式细菌中建立的规则，即通过沿着细胞长度插入新物质来生长；相反，许多病原体从它们的极点生长。致病菌还携带多部分基因组，以适应不同的生态位。在极性生长的背景下，多染色体如何复制和分离在很大程度上是未知的。在这里，植物病原体农杆菌的四个复制子在极性生长周期中表现出不同的时间和空间复制/分离模式，并且针对未生长和新生长极点的特定蛋白质调节复制子的传播。揭示极性生长和染色体分离的机制将为设计限制细菌性疾病的策略提供新的机会。农杆菌C58含有4个复制子，分别为圆形染色体（CC）、线性染色体（LC）、隐质粒（pAt）和肿瘤诱导质粒（pTi），由单生长极（GP）进行极性生长，旧细胞室及其旧极（OP）不伸长。我们监测了这四种遗传因子在极性生长过程中的复制和分离。三个最大的复制子（CC， LC, pAt）在复制前存在于OP区；复制后，一个副本在分割前迁移到GP。CC位于OP的固定位置，并首先进行复制。一旦细胞周期开始，LC就不会固定在OP，并且比cc晚20分钟从不同的位置复制。pAt在复制前的定位与LC相似，但在LC之前和cc之后复制。pTi没有固定的位置，复制后它在新旧细胞区室中随机分离，同时在单个细胞周期中进行一到三轮复制。CC和LC的分离分别取决于GP和OP的身份因子PopZ和PodJ。没有PopZ，复制的CC和LC不能有效地分裂，导致没有CC或LC的同胞细胞。没有PodJ， CC和LC在细胞周期开始时表现出异常的GP定位，并从这个位置复制。这些数据表明，在极地生长的早期阶段，PodJ在CC和LC与OP的捆绑中起着重要作用。
Significance Bacteria are ubiquitous, essential, and remarkably diverse. Many infectious species do not follow rules established in model bacteria where growth occurs by insertion of new material along the cell length; instead, many pathogens grow from their poles. Pathogenic bacteria also carry multipartite genomes for adaptation to different ecological niches. How multiple chromosomes replicate and segregate in the context of polar growth is largely unknown. Here, four replicons of the plant pathogen Agrobacterium tumefaciens exhibit distinct temporal and spatial replication/segregation patterns during the polar growth cycle, and specific proteins, targeted to the nongrowing and new growth poles, regulate replicon transmission. Uncovering the mechanisms underlying polar growth and chromosome segregation will present new opportunities to design strategies to limit bacterial diseases. Agrobacterium tumefaciens C58 contains four replicons, circular chromosome (CC), linear chromosome (LC), cryptic plasmid (pAt), and tumor-inducing plasmid (pTi), and grows by polar growth from a single growth pole (GP), while the old cell compartment and its old pole (OP) do not elongate. We monitored the replication and segregation of these four genetic elements during polar growth. The three largest replicons (CC, LC, pAt) reside in the OP compartment prior to replication; post replication one copy migrates to the GP prior to division. CC resides at a fixed location at the OP and replicates first. LC does not stay fixed at the OP once the cell cycle begins and replicates from varied locations 20 min later than CC. pAt localizes similarly to LC prior to replication, but replicates before the LC and after the CC. pTi does not have a fixed location, and post replication it segregates randomly throughout old and new cell compartments, while undergoing one to three rounds of replication during a single cell cycle. Segregation of the CC and LC is dependent on the GP and OP identity factors PopZ and PodJ, respectively. Without PopZ, replicated CC and LC do not efficiently partition, resulting in sibling cells without CC or LC. Without PodJ, the CC and LC exhibit abnormal localization to the GP at the beginning of the cell cycle and replicate from this position. These data reveal PodJ plays an essential role in CC and LC tethering to the OP during early stages of polar growth.