Universität Rostock, Institut für Biowissenschaften, Pflanzenphysiologie, Albert-Einstein-Str. 3, D-18059 Rostock, Germany.
Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Golm, Germany.
Microbiology (Reading). 2012 Feb;158(Pt 2):398-413. doi: 10.1099/mic.0.054544-0. Epub 2011 Nov 17.
Using metabolic and transcriptomic phenotyping, we studied acclimation of cyanobacteria to low inorganic carbon (LC) conditions and the requirements for coordinated alteration of metabolism and gene expression. To analyse possible metabolic signals for LC sensing and compensating reactions, the carboxysome-less mutant ΔccmM and the photorespiratory mutant ΔglcD1/D2 were compared with wild-type (WT) Synechocystis. Metabolic phenotyping revealed accumulation of 2-phosphoglycolate (2PG) in ΔccmM and of glycolate in ΔglcD1/D2 in LC- but also in high inorganic carbon (HC)-grown mutant cells. The accumulation of photorespiratory metabolites provided evidence for the oxygenase activity of RubisCO at HC. The global gene expression patterns of HC-grown ΔccmM and ΔglcD1/D2 showed differential expression of many genes involved in photosynthesis, high-light stress and N assimilation. In contrast, the transcripts of LC-specific genes, such as those for inorganic carbon transporters and components of the carbon-concentrating mechanism (CCM), remained unchanged in HC cells. After a shift to LC, ΔglcD1/D2 and WT cells displayed induction of many of the LC-inducible genes, whereas ΔccmM lacked similar changes in expression. From the coincidence of the presence of 2PG in ΔccmM without CCM induction and of glycolate in ΔglcD1/D2 with CCM induction, we regard a direct role for 2PG as a metabolic signal for the induction of CCM during LC acclimation as less likely. Instead, our data suggest a potential role for glycolate as a signal molecule for enhanced expression of CCM genes.
利用代谢组学和转录组学表型分析，我们研究了蓝藻对低无机碳（LC）条件的适应以及代谢和基因表达协同改变的要求。为了分析 LC 感应和补偿反应的可能代谢信号，我们比较了无羧化酶体突变体 ΔccmM 和光呼吸突变体 ΔglcD1/D2 与野生型（WT）集胞藻。代谢表型分析显示，2-磷酸甘油酸（2PG）在 LC 条件下且在高无机碳（HC）条件下在 ΔccmM 中积累，而在 ΔglcD1/D2 中积累了光呼吸代谢物。RubisCO 加氧酶活性在 HC 条件下提供了证据。HC 生长的 ΔccmM 和 ΔglcD1/D2 的全局基因表达模式显示，许多参与光合作用、高光胁迫和 N 同化的基因表达存在差异。相比之下，LC 特异性基因，如无机碳转运体和碳浓缩机制（CCM）的组成部分的转录物在 HC 细胞中保持不变。在转移到 LC 后，ΔglcD1/D2 和 WT 细胞显示出许多 LC 诱导基因的诱导，而 ΔccmM 缺乏类似的表达变化。由于 ΔccmM 中没有 CCM 诱导但存在 2PG，以及 ΔglcD1/D2 中存在 CCM 诱导但存在 2PG，我们认为 2PG 作为 LC 适应期间 CCM 诱导的代谢信号不太可能直接发挥作用。相反，我们的数据表明，甘氨酸可能作为增强 CCM 基因表达的信号分子发挥作用。
