No abstract

Potato (Solanum tuberosum L.) is a major crop worldwide that meets human economic and nutritional requirements. Potato has several advantages over other crops: easy to cultivate and store, cheap to consume, and rich in a variety of secondary metabolites. In this study, we generated three marker-free transgenic potato lines that expressed the Arabidopsis thaliana flavonol-specific transcriptional activator AtMYB12 driven by the tuber-specific promoter Patatin. Marker-free potato tubers displayed increased amounts of caffeoylquinic acids (CQAs) (3.35-fold increases on average) and flavonols (4.50-fold increase on average). Concentrations of these metabolites were associated with the enhanced expression of genes in the CQA and flavonol biosynthesis pathways. Accumulation of CQAs and flavonols resulted in 2-fold higher antioxidant capacity compared to wild-type potatoes. Tubers from these marker-free transgenic potatoes have therefore improved antioxidant properties.

Escherichia coli strain K-12 MG1655 has been proposed as an appropriate host strain for industrial production. However, the direct application of this strain suffers from the transformation inefficiency and plasmid instability. Herein, we conducted genetic modifications at a serial of loci of MG1655 genome, generating a robust and universal host strain JW128 with higher transformation efficiency and plasmid stability that can be used to efficiently produce desired chemicals after introducing the corresponding synthetic pathways. Using JW128 as the host, the titer of isobutanol reached 5.76 g/L in shake-flask fermentation, and the titer of lycopene reached 1.91 g/L in test-tube fermentation, 40-fold and 5-fold higher than that of original MG1655, respectively. These results demonstrated JW128 is a promising chassis for high-level production of value-added chemicals.

Background: Protein-based bioconversion has been demonstrated as a sustainable approach to produce higher alcohols and ammonia fertilizers. However, owing to the switchover from transcription mediated by the bacterial RNA polymerase σ 70 to that mediated by alternative σ factors, the biofuel production driven by σ 70-dependent promoters declines rapidly once cells enter the stationary phase or encounter stresses. To enhance biofuel production, in this study the growth phase-independent and nitrogen-responsive transcriptional machinery mediated by the σ 54 is exploited to drive robust protein-to-fuel conversion. Results: We demonstrated that disrupting the Escherichia coli ammonia assimilation pathways driven by glutamate dehydrogenase and glutamine synthetase could sustain the activity of σ 54-mediated transcription under ammoniaaccumulating conditions. In addition, two σ 54-dependent promoters, argTp and glnAp2, were identified as suitable candidates for driving pathway expression. Using these promoters, biofuel production from proteins was shown to persist to the stationary phase, with the net production in the stationary phase being 1.7-fold higher than that derived from the optimal reported σ 70-dependent promoter P L lacO 1. Biofuel production reaching levels 1.3-to 3.4-fold higher than those of the σ 70-dependent promoters was also achieved by argTp and glnAp2 under stressed conditions. Moreover, the σ 54-dependent promoters realized more rapid and stable production than that of σ 70-dependent promoters during fed-batch fermentation, producing up to 4.78 g L − 1 of total biofuels. Conclusions: These results suggested that the nitrogen-responsive transcriptional machinery offers the potential to decouple production from growth, highlighting this system as a novel candidate to realize growth phase-independent and stress-resistant biofuel production.