Time-series resolution of gradual nitrogen starvation and its impact on photosynthesis in the cyanobacterium Synechocystis PCC 6803
Time-series resolution of gradual nitrogen starvation and its impact on photosynthesis in the cyanobacterium Synechocystis PCC 6803
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DOI：
10.1111/j.1399-3054.2012.01585.x
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发表时间：
2012-07-01
影响因子：
6.4
通讯作者：
Matthijs, Hans C. P.
中科院分区：
文献类型：
--
作者：
Krasikov, Vladimir;Aguirre von Wobeser, Eneas;Matthijs, Hans C. P.
对氮剥夺和最终完全饥饿的连续适应需要细胞功能的协调调节。我们研究了蓝藻集胞藻PCC 6803在96小时的氮饥饿的基因表达和细胞生理的变化。在第一个6小时，转录组显示氮吸收和同化系统的核心氮和碳同化调节剂的激活。然而，氮剥夺的细胞仍然以与对照相同的速率生长，甚至表现出短暂的藻胆体基因表达增加。12小时后，细胞生长下降，并开始褪绿与富氮藻胆体的降解。在此阶段，转录组显示抑制藻胆体，碳固定和从头蛋白质合成的基因。有趣的是，光系统I（PSI）和光系统II的光合活性保留得很好。通过末端氧化酶和氢化酶基因的诱导，过量的电子被淬灭，补偿了减少的碳固定和硝酸盐还原活性。48 h后，细胞基本停止活动。一个明显的例外是保留PSI基因转录，这可能支持集胞藻细胞的活力，并使氮饥饿后迅速恢复。在早期恢复过程中，许多基因改变了表达，支持恢复细胞活性。总的来说，我们的研究结果区分了三个阶段，在逐步氮耗竭：（1）立即反应，（2）短期驯化和（3）长期生存。这表明蓝藻对氮饥饿的反应是通过一系列生理适应来实现的，这些生理适应通过转录组在不同时间尺度上展开的许多变化来反映。
Sequential adaptation to nitrogen deprivation and ultimately to full starvation requires coordinated adjustment of cellular functions. We investigated changes in gene expression and cell physiology of the cyanobacterium Synechocystis PCC 6803 during 96 h of nitrogen starvation. During the first 6 h, the transcriptome showed activation of nitrogen uptake and assimilation systems and of the core nitrogen and carbon assimilation regulators. However, the nitrogen-deprived cells still grew at the same rate as the control and even showed transiently increased expression of phycobilisome genes. After 12 h, cell growth decreased and chlorosis started with degradation of the nitrogen-rich phycobilisomes. During this phase, the transcriptome showed suppression of genes for phycobilisomes, for carbon fixation and for de novo protein synthesis. Interestingly, photosynthetic activity of both photosystem I (PSI) and photosystem II was retained quite well. Excess electrons were quenched by the induction of terminal oxidase and hydrogenase genes, compensating for the diminished carbon fixation and nitrate reduction activity. After 48 h, the cells ceased most activities. A marked exception was the retained PSI gene transcription, possibly this supports the viability of Synechocystis cells and enables rapid recovery after relieving from nitrogen starvation. During early recovery, many genes changed expression, supporting the resumed cellular activity. In total, our results distinguished three phases during gradual nitrogen depletion: (1) an immediate response, (2) short-term acclimation and (3) long-term survival. This shows that cyanobacteria respond to nitrogen starvation by a cascade of physiological adaptations reflected by numerous changes in the transcriptome unfolding at different timescales.