cyAbrB Transcriptional Regulators as Safety Devices To Inhibit Heterocyst Differentiation in Anabaena sp. Strain PCC 7120
cyAbrB Transcriptional Regulators as Safety Devices To Inhibit Heterocyst Differentiation in Anabaena sp. Strain PCC 7120
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DOI：
10.1128/jb.00244-19
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发表时间：
2019-09-01
影响因子：
3.2
通讯作者：
Ehira, Shigeki
中科院分区：
文献类型：
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作者：
Higo, Akiyoshi;Nishiyama, Eri;Ehira, Shigeki
蓝细菌是进行产氧光合作用的单系生物。虽然它们表现出很大的多样性，但它们有一组共同的基因。然而，它们对于生存力的重要性阻碍了对其功能的阐明。这些基因的一个例子是cyabrB 1（在鱼腥藻属菌株PCC 7120中也称为calA），其编码转录调节因子。在本研究中，我们通过CRISPR干扰研究了caIA/cyabrBl在形成杂囊的蓝藻Anabaena sp. PCC 7120中的功能，这是我们最近在该菌株中用于光合生产有用化学物质的方法。在硝酸盐的存在下，calA/cyabrB 1的条件敲低导致异形胞的形成。两个基因，hetP和hepA，这是所需的异形胞形成，上调caIA/cyabrB 1敲低的存在下，结合氮源。已知这些基因由HetR诱导，HetR是异形胞形成的主要调节因子。calA/cyabrB 1敲低不诱导hetR。CalA/cyAbrB 1以HetR非依赖性方式直接结合其启动子区，从而抑制hetP和hepA。此外，过表达calA/cyabrB 1废除异形胞形成氮耗尽。此外，敲除calB/cyabrB 2（calA/cyabrB 1的一个同源基因），除了敲除calA/cyabrB 1，增强异胞形成在硝酸盐的存在下，这表明cyAbrB蛋白的功能冗余。我们认为，HetR和CalA/cyAbrB 1的数量之间的平衡是一个关键因素，影响异形胞分化过程中的氮降压。我们得出结论，cyAbrB蛋白是必不可少的安全装置，抑制异形胞differentiation.IMPORTANCE枯草芽孢杆菌和链霉菌的孢子形成已被广泛研究作为模型的原核非末端细胞分化。在这些生物体中，许多细胞/菌丝同时分化，这是由一个网络控制的，其中一个调节器位于顶部。鱼腥藻菌株PCC 7120中异形胞的分化是独特的，因为它是末端的，并且只有5%至10%的营养细胞分化成异形胞。在这项研究中，我们确定了CalA/cyAbrB 1作为两个基因的阻遏物，这两个基因是独立的HetR，一个主激活异形胞分化的异形胞形成所必需的。这一发现对于鱼腥藻独特的细胞分化是合理的，因为CalA/cyAbrB 1可以紧密地抑制营养细胞中的异形胞分化，而只有HetR过表达的细胞才能分化成异形胞。
Cyanobacteria are monophyletic organisms that perform oxygenic photosynthesis. While they exhibit great diversity, they have a common set of genes. However, the essentiality of them for viability has hampered the elucidation of their functions. One example of these genes is cyabrB1 (also known as calA in Anabaena sp. strain PCC 7120), encoding a transcriptional regulator. In the present study, we investigated the function of caIA/cyabrBl in the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 through CRISPR interference, a method that we recently utilized for the photosynthetic production of a useful chemical in this strain. Conditional knockdown of calA/cyabrB1 in the presence of nitrate resulted in the formation of heterocysts. Two genes, hetP and hepA, which are required for heterocyst formation, were upregulated by caIA/cyabrB1 knockdown in the presence of combined nitrogen sources. These genes are known to be induced by HetR, a master regulator of heterocyst formation. hetR was not induced by calA/cyabrB1 knockdown. hetP and hepA were repressed by direct binding of CalA/cyAbrB1 to their promoter regions in a HetR-independent manner. In addition, the overexpression of calA/cyabrB1 abolished heterocyst formation upon nitrogen depletion. Also, knockout of calB/cyabrB2 (a paralogue gene of calA/cyabrB1), in addition to knockdown of calA/ cyabrB1, enhanced heterocyst formation in the presence of nitrate, suggesting functional redundancy of cyAbrB proteins. We propose that a balance between amounts of HetR and CalA/cyAbrB1 is a key factor influencing heterocyst differentiation during nitrogen stepdown. We concluded that cyAbrB proteins are essential safety devices that inhibit heterocyst differentiation.IMPORTANCE Spore formation in Bacillus subtilis and Streptomyces has been extensively studied as models of prokaryotic nonterminal cell differentiation. In these organisms, many cells/hyphae differentiate simultaneously, which is governed by a network in which one regulator stands at the top. Differentiation of heterocysts in Anabaena sp. strain PCC 7120 is unique because it is terminal, and only 5 to 10% of vegetative cells differentiate into heterocysts. In this study, we identified CalA/cyAbrB1 as a repressor of two genes that are essential for heterocyst formation independently of HetR, a master activator for heterocyst differentiation. This finding is reasonable for unique cell differentiation of Anabaena because CalA/cyAbrB1 could suppress heterocyst differentiation tightly in vegetative cells, while only cells in which HetR is overexpressed could differentiate into heterocysts.