The rare actinomycete Actinoplanes missouriensis forms sporangia, which open up and release zoospores in response to water. Here, we report a genetic and functional analysis of four FliA‐family sigma factors, FliA1, FliA2, FliA3 and FliA4. Transcription of fliA1 , fliA2 and fliA3 was directly activated by the global transcriptional activator TcrA during sporangium formation and dehiscence, while fliA4 was almost always transcribed at low levels. Gene disruption analysis showed that (a) deletion of fliA2 reduced the zoospore swimming speed by half, (b) the fliA1 ‐fliA2 double‐deletion mutant formed abnormal sporangia in which mutant spores ectopically germinated and (c) deletion of fliA3 induced no phenotypic changes in the wild‐type and mutant strains of fliA1 and/or fliA2 . Comparative RNA‐Seq analyses among the wild‐type and gene deletion mutant strains showed probable targets of each FliA‐family sigma factor, indicating that FliA1‐ and FliA2‐dependent promoters are quite similar to each other, while the FliA3‐dependent promoter is somewhat different. Gene complementation experiments also indicated that the FliA1 regulon overlaps with the FliA2 regulon. These results demonstrate that A. missouriensis has developed a complex transcriptional regulatory network involving multiple FliA‐family sigma factors for the accomplishment of its characteristic reproduction process, including sporangium formation, spore dormancy and sporangium dehiscence.

中文翻译：

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三个FliA家族σ因子参与密苏里放线放线菌的孢子形成，孢子休眠和孢子裂开。

稀有的放线菌放线菌密苏里州形成孢子囊，其响应水而开放并释放游动孢子。在这里，我们报告了四个FliA家庭sigma因子FliA1，FliA2，FliA3和FliA4的遗传和功能分析。转录fliA1，fliA2和fliA3直接通过在孢子囊的形成和裂开全球转录激活活性TCRA，而fliA4在较低水平几乎总是转录。基因破坏分析表明（a）fliA2的缺失使游动孢子的游泳速度降低了一半，（b）fliA1 - fliA2双缺失突变体形成异常的孢子囊，其中突变体孢子异位萌发，（c）fliA3的缺失在fliA1和/或fliA2的野生型和突变株中不引起表型变化。在野生型和基因缺失突变株之间进行的比较RNA‐Seq分析显示，每个FliA家族sigma因子可能都是靶标，表明FliA1和FliA2依赖的启动子彼此非常相似，而FliA3依赖的启动子有些相似不同。基因互补实验还表明，FliA1调节子与FliA2调节子重叠。这些结果表明密苏里州曲霉 已开发出涉及多个FliA家族sigma因子的复杂转录调控网络，以完成其特征性繁殖过程，包括孢子囊形成，孢子休眠和孢子囊裂开。