Multicellular organisms implement a set of reactions involving signaling and cooperation between different types of cells. Unicellular organisms, on the other hand, activate defense systems that involve collective behaviors between individual organisms. In the unicellular model alga Chlamydomonas (Chlamydomonas reinhardtii), the existence and the function of collective behaviors mechanisms in response to stress remain mostly at the level of the formation of small structures called palmelloids. Here, we report the characterization of a mechanism of abiotic stress response that Chlamydomonas can trigger to form massive multicellular structures. We showed that these aggregates constitute an effective bulwark within which the cells are efficiently protected from the toxic environment. We generated a family of mutants that aggregate spontaneously, the socializer (saz) mutants, of which saz1 is described here in detail. We took advantage of the saz mutants to implement a large-scale multiomics approach that allowed us to show that aggregation is not the result of passive agglutination, but rather genetic reprogramming and substantial modification of the secretome. The reverse genetic analysis we conducted allowed us to identify positive and negative regulators of aggregation and to make hypotheses on how this process is controlled in Chlamydomonas.

中文翻译：

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非生物胁迫诱导的社会化如何导致衣藻中大量聚集体的形成。

多细胞生物体执行一系列涉及不同类型细胞之间的信号传导和合作的反应。另一方面，单细胞生物激活涉及个体生物之间集体行为的防御系统。在单细胞模型藻类衣藻（Chlamydomonas Reinhardtii）中，响应压力的集体行为机制的存在和功能主要停留在形成称为棕榈状体的小结构的水平上。在这里，我们报告了衣藻可以触发形成大量多细胞结构的非生物应激反应机制的特征。我们表明，这些聚集体构成了有效的堡垒，在其中细胞可以有效地免受有毒环境的影响。我们产生了一个自发聚集的突变体家族，社交者 (saz) 突变体，其中 saz1 在此详细描述。我们利用 saz 突变体实施大规模多组学方法，使我们能够证明聚集不是被动凝集的结果，而是遗传重编程和分泌组的实质性修饰的结果。我们进行的反向遗传分析使我们能够识别聚集的正向和负向调节因子，并就衣藻中如何控制这一过程做出假设。