4CO₂+5H₂O→CH₃CH₂CH₂CH₂OH+6O₂

Note, the DNA sequences encoding for the enzymes of the designer pathway (branched from the Calvin cycle at the point of 3-phosphoglycerate) including phosphoglyerate mutase, enolase, pyruvate kinase, pyruvate-ferredoxin oxidoreductase, thiolase, 3-hydroxybutyryl-CoA dehydrogenase, crotonase, butyryl-CoA dehydrogenase, butyraldehyde dehydrogenase, and butanol dehydrogenase, are now all known. Therefore, this type of designer pathways can be readily constructed through application of synthetic biology using synthetic transgenes.

This type of photobiological biofuels-production process completely eliminates the problem of recalcitrant lignocellulosics by bypassing the bottleneck problem of the biomass technology, since this approach could theoretically produce biofuels (such as butanol) directly from water and carbon dioxide with high solar-to-biofuel energy efficiency. According to a recent study [4] for this type of direct photosynthesis-to-biofuel process, the practical maximum solar-to-biofuel energy conversion efficiency could be about 7.2% while the theoretical maximum solar-tobiofuel energy conversion efficiency is calculated to be 12%.

The designer algae approach may also enable the use of seawater and/or groundwater for photobiological production of biofuels without requiring freshwater or agricultural soil, since the biofuel-producing function can be placed through molecular genetics into certain marine algae and/or cyanobacteria that can use seawater and/or certain groundwater. They may be used also in a sealed photobioreactor that could be operated on a desert for production of biofuels with highly efficient use of water since there will be little or no water loss by evaporation and/or transpiration that a common crop system would suffer. That is, this designer algae approach could provide a new generation of renewable energy (e.g., butanol) production technology without requiring arable land or freshwater resources, which may be strategically important to many parts of the world for long-term sustainable development. Recently, certain independent studies [5-7] have also applied synthetic biology in certain model cyanobacteria such as Synecoccus elongatus PCC7942 for photobiological production of isobutanol and 1-butanol.

Furthermore, the designer algae approach may be applied for enhanced photobiological production of other bioproducts including (but not limited to) high-value bioproducts, such as pharmaceuticalsrelated products: DHA (docosahexaenoic acid) omega-3 fatty acid, EPA (eicosapentaenoic acid) omega-3 fatty acid, ARA (arachidonic acid) omega-6 fatty acid, chlorophylls, carotenoids, phycocyanins, allophycocyanin, phycoerythrin, and their derivatives/related product species.

The biosafety issue as in any other molecular genetics manipulations is also a significant challenge and research opportunity for application of synthetic biology in plant biochemistry and physiology. With proper application of synthetic biology techniques, it is also possible to address this issue. For example, certain biosafety-guarded features [6] may be developed with the application of synthetic biology that could prevent transgenic algae from exchanging their genetic materials with any other organisms to ensure biosafety.

In summary, proper application of synthetic biology with plant cells may provide a significant research opportunity in developing advanced biofuels and bioproducts as part of the solutions towards sustainability on Earth. The emerging synthetic biology with increased demands for energy and sustainability may re-energize the field of Plant Biochemistry & Physiology.