Abstract
The development of high-throughput technology using RNA-seq has allowed understanding of cellular mechanisms and regulations of bacterial transcription. In addition, transcriptome analysis with RNA-seq has been used to accelerate strain improvement through systems metabolic engineering. Synechococcus elongatus PCC 7942, a photosynthetic bacterium, has remarkable potential for biochemical and biofuel production due to photoautotrophic cell growth and direct CO2 conversion. Here, we performed a transcriptome analysis of S. elongatus PCC 7942 using RNA-seq to understand the changes of cellular metabolism and regulation for nitrogen starvation responses. As a result, differentially expressed genes (DEGs) were identified and functionally categorized. With mapping onto metabolic pathways, we probed transcriptional perturbation and regulation of carbon and nitrogen metabolisms relating to nitrogen starvation responses. Experimental evidence such as chlorophyll a and phycobilisome content and the measurement of CO2 uptake rate validated the transcriptome analysis. The analysis suggests that S. elongatus PCC 7942 reacts to nitrogen starvation by not only rearranging the cellular transport capacity involved in carbon and nitrogen assimilation pathways but also by reducing protein synthesis and photosynthesis activities.
Highlights
Global concerns about energy security and environmental issues affecting climate changes have focused attention on engineering photosynthetic organisms that are able to sequester and convert CO2 to organic materials using solar energy[1,2]
Cyanobacterial cell growth was stopped under a N− condition only, resulting in chlorosis of cells after days of starvation in the medium (Fig. 1), which has been shown previously[25]
We analyzed the transcriptome of S. elongatus PCC 7942 for nitrogen starvation responses using RNA-seq
Summary
Global concerns about energy security and environmental issues affecting climate changes have focused attention on engineering photosynthetic organisms that are able to sequester and convert CO2 to organic materials using solar energy[1,2]. It is important to understand the positive and negative mechanisms of nitrogen regulation in a cell for system-wide strain development. The nitrogen starvation response of cyanobacteria including Synechococcus elongatus PCC 7942 as a cyanobacterial model organism has been studied to understand the mechanisms of degradation of phycobiliproteins[14] and its consequent induction of chlorosis[15,16]. The signal transduction protein PII and the regulator PipX (PII interacting protein X) modulate the gene expression in nitrogen control in S. elongatus PCC 794220,21. A global transcriptomic analysis of S. elongatus PCC 7942 has not been available yet for the nitrogen starvation response a comprehensive analysis of S. elongatus PCC 7942 using ChIP-seq, RNA-seq, and tiling expression microarray has been reported[24]
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