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首页> 外文期刊>Journal of Experimental Botany >Regulation of nitrate assimilation in cyanobacteria
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Regulation of nitrate assimilation in cyanobacteria

机译：蓝细菌中硝酸盐同化的调节

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Nitrate assimilation by cyanobacteria is inhibited by the presence of ammonium in the growth medium. Both nitrate uptake and transcription of the nitrate assimilatory genes are regulated. The major intracellular signal for the regulation is, however, not ammonium or glutamine, but 2-oxoglutarate (2-OG), whose concentration changes according to the change in cellular C/N balance. When nitrogen is limiting growth, accumulation of 2-OG activates the transcription factor NtcA to induce transcription of the nitrate assimilation genes. Ammonium inhibits transcription by quickly depleting the 2-OG pool through its metabolism via the glutamine synthetase/glutamate synthase cycle. The P-II protein inhibits the ABC-type nitrate transporter, and also nitrate reductase in some strains, by an unknown mechanism(s) when the cellular 2-OG level is low. Upon nitrogen limitation, 2-OG binds to P-II to prevent the protein from inhibiting nitrate assimilation. A pathway-specific transcriptional regulator NtcB activates the nitrate assimilation genes in response to nitrite, either added to the medium or generated intracellularly by nitrate reduction. It plays an important role in selective activation of the nitrate assimilation pathway during growth under a limited supply of nitrate. P-II was recently shown to regulate the activity of NtcA negatively by binding to PipX, a small coactivator protein of NtcA. On the basis of accumulating genome information from a variety of cyanobacteria and the molecular genetic data obtained from the representative strains, common features and group- or species-specific characteristics of the response of cyanobacteria to nitrogen is summarized and discussed in terms of ecophysiological significance.
机译：生长培养基中铵的存在抑制了蓝藻对硝酸盐的吸收。硝酸盐吸收和硝酸盐同化基因的转录均受到调节。然而，用于调节的主要细胞内信号不是铵或谷氨酰胺，而是2-氧代戊二酸酯（2-OG），其浓度根据细胞C / N平衡的变化而变化。当氮限制生长时，2-OG的积累会激活转录因子NtcA，以诱导硝酸盐同化基因的转录。铵通过谷氨酰胺合成酶/谷氨酸合酶循环通过其代谢迅速消耗2-OG库来抑制转录。当细胞2-OG水平低时，P-II蛋白会通过未知机制抑制ABC型硝酸盐转运蛋白，并在某些菌株中抑制硝酸盐还原酶。在氮限制下，2-OG与P-II结合以防止蛋白质抑制硝酸盐同化。特定于途径的转录调节因子NtcB响应亚硝酸盐而激活硝酸盐同化基因，亚硝酸盐可以添加到培养基中，也可以通过硝酸盐还原在细胞内生成。在有限的硝酸盐供应下生长期间，它在选择性激活硝酸盐同化途径中起重要作用。最近显示，P-II通过与PipX（NtcA的一种小辅助激活蛋白）结合而负调控NtcA的活性。在积累各种蓝细菌的基因组信息和从代表性菌株获得的分子遗传数据的基础上，从生态生理学意义上总结和讨论了蓝细菌对氮的反应的共同特征和群体或物种特异性特征。

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