期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：50
页码：14225-14230
DOI：10.1073/pnas.1613340113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceLife on Earth depends on photosynthesis to capture solar energy and reduce CO2 into organic carbons. One strategy to improve photosynthesis is to enhance carbon assimilation by "nonnative" carbon sinks (e.g., terpene biosynthesis). Previous attempts to enhance terpene biosynthesis in photosynthetic organisms have met with limited success. Through computational modeling and synthetic biology tools, we identified and overcame a key flux-controlling node in 2-C-methyl-D-erythritol 4-phosphate-derived terpene biosynthesis in cyanobacteria. This strategy bypasses the limitation in traditional stepwise metabolic engineering, and enables record limonene productivity. The breakthrough allowed systems biology analysis to reveal photosynthesis regulations under a high level of limonene production. Fine-tuning energy and reductant requirement could be a key factor to further synergize photosynthesis and terpene production. Terpenes are the major secondary metabolites produced by plants, and have diverse industrial applications as pharmaceuticals, fragrance, solvents, and biofuels. Cyanobacteria are equipped with efficient carbon fixation mechanism, and are ideal cell factories to produce various fuel and chemical products. Past efforts to produce terpenes in photosynthetic organisms have gained only limited success. Here we engineered the cyanobacterium Synechococcus elongatus PCC 7942 to efficiently produce limonene through modeling guided study. Computational modeling of limonene flux in response to photosynthetic output has revealed the downstream terpene synthase as a key metabolic flux-controlling node in the MEP (2-C-methyl-D-erythritol 4-phosphate) pathway-derived terpene biosynthesis. By enhancing the downstream limonene carbon sink, we achieved over 100-fold increase in limonene productivity, in contrast to the marginal increase achieved through stepwise metabolic engineering. The establishment of a strong limonene flux revealed potential synergy between photosynthate output and terpene biosynthesis, leading to enhanced carbon flux into the MEP pathway. Moreover, we show that enhanced limonene flux would lead to NADPH accumulation, and slow down photosynthesis electron flow. Fine-tuning ATP/NADPH toward terpene biosynthesis could be a key parameter to adapt photosynthesis to support biofuel/bioproduct production in cyanobacteria.
