Filamentous cyanobacteria represent model organisms for investigating multicellularity. For many species, nitrogen-fixing heterocysts are formed from photosynthetic vegetative cells under nitrogen limitation. Intracellular Ca2+ has been implicated in the highly regulated process of heterocyst differentiation but its role remains unclear. Ca2+ is known to operate more broadly in metabolic signalling in cyanobacteria, although the signalling mechanisms are virtually unknown. A Ca2+-binding protein called the Ca2+ Sensor EF-hand (CSE) is found almost exclusively in filamentous cyanobacteria. Expression of asr1131 encoding the CSE protein in Anabaena sp. PCC 7120 was strongly induced by low CO2 conditions, and rapidly downregulated during nitrogen step-down. A previous study suggests a role for CSE and Ca2+ in regulation of photosynthetic activity in response to changes in carbon and nitrogen availability. In the current study, a mutant Anabaena sp. PCC 7120 strain lacking asr1131 (Δcse) was highly prone to filament fragmentation, leading to a striking phenotype of very short filaments and poor growth under nitrogen-depleted conditions. Transcriptomics analysis under nitrogen-replete conditions revealed that genes involved in heterocyst differentiation and function were downregulated in Δcse, while heterocyst inhibitors were upregulated, compared to the wild-type. These results indicate that CSE is required for filament integrity and for proper differentiation and function of heterocysts upon changes in the cellular carbon/nitrogen balance. A role for CSE in transmitting Ca2+ signals during the first response to changes in metabolic homeostasis is discussed.

中文翻译：

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小的Ca2 +结合蛋白CSE将Ca2 +信号传导与Anabaena sp。中的氮代谢和细丝完整性联系起来。PCC 7120。

丝状蓝细菌代表用于研究多细胞性的模型生物。对于许多物种而言，固氮的异质囊是在氮限制下由光合营养细胞形成的。细胞内Ca 2+已经参与了高度调控的异胚细胞分化过程，但其作用尚不清楚。尽管实际上尚不清楚Ca2 +在蓝细菌的代谢信号传导中的作用，但其作用机制却很广。几乎仅在丝状蓝细菌中发现了一种称为Ca2 +传感器EF-hand（CSE）的Ca2 +结合蛋白。编码CSE蛋白的asr1131在鱼腥藻中的表达。PCC 7120在低CO2条件下强烈诱导，并在氮气降压过程中迅速下调。先前的一项研究表明，CSE和Ca2 +在响应碳和氮可利用性变化时在调节光合作用活动中发挥作用。在当前的研究中，一个突变的鱼腥藻。缺少asr1131（Δcse）的PCC 7120菌株极易发生细丝断裂，导致非常短的细丝具有明显的表型，并且在氮贫化条件下生长不良。与野生型相比，在充氮条件下的转录组学分析显示，与Δcse相比，参与杂种囊分化和功能的基因被下调，而杂种抑制剂被上调。这些结果表明，当细胞碳/氮平衡发生变化时，CSE对于细丝完整性以及适当的异型囊肿分化和功能是必需的。