Overexpression of artificially fused bifunctional enzyme 4CL1-CCR: a method for production of secreted 4-hydroxycinnamaldehydes in Escherichia coli

Fusion gene 4CL-CCR promotes lignification in tobacco suspension cells

KEY MESSAGE

The fusion gene 4CL-CCR promotes lignification and activates lignin-related MYB expression in tobacco but inhibits auxin-related gene expression and hinders the auxin absorption of cells. Given the importance of lignin polymers in plant growth and their industrial value, it is necessary to investigate how plants synthesize monolignols and regulate the level of lignin in cell walls. In our previous study, expression of the Populus tomentosa fusion gene 4CL-CCR significantly promoted the production of 4-hydroxycinnamyl alcohols. However, the function of 4CL-CCR in organisms remains poorly understood. In this study, the fusion gene 4CL-CCR was heterologously expressed in tobacco suspension cells. We found that the transgenic suspension cells exhibited lignification earlier. Furthermore, 4CL-CCR significantly reduced the content of phenolic acids and increased the content of aldehydes in the medium, which led to an increase in lignin deposition. Moreover, transcriptome results showed that the genes related to lignin synthesis, such as PAL, 4CL, CCoAOMT and CAD, were significantly upregulated in the 4CL-CCR group. The expression of genes related to auxin, such as ARF3, ARF5 and ARF6, was significantly downregulated. The downregulation of auxin affected the expression of transcription factor MYBs. We hypothesize that the upregulated genes MYB306 and MYB315 are involved in the regulation of cell morphogenesis and lignin biosynthesis and eventually enhance lignification in tobacco suspension cells. Our findings provide insight into the function of 4CL-CCR in lignification and how secondary cell walls are formed in plants.

The Streptomyces scabiei Pathogenicity Factor Thaxtomin A Induces the Production of Phenolic Compounds in Potato Tubers

The phytotoxin thaxtomin A (TA) is the key pathogenicity factor synthesized by the bacteria Streptomyces scabiei, the main causal agent of common scab of potato (Solanum tuberosum L.). TA treatment of potato tuber flesh produces a brown color that was attributed to necrosis. The intensity of TA-induced browning was generally thought to correlate with potato sensitivity to the disease. In this study, we found that TA-induced browning was much more intense in the potato tuber flesh of the common scab moderately resistant variety Russet Burbank (RB) than that observed in tubers of the disease-susceptible variety Yukon Gold (YG). However, there was no significant difference in the level of TA-induced cell death detected in both varieties, suggesting that tubers response to TA does not correlate with the level of sensitivity to common scab. TA-treated potato tuber tissues accumulated significantly higher levels of phenolic compounds than untreated controls, with a higher phenol content detected in RB TA-treated tissues than in those of YG. Browning was associated with a significant induction of the expression of genes of the phenylpropanoid pathway in RB tubers, indicating that TA activated this metabolic pathway. These results suggest that tuber flesh browning induced by TA is due to the accumulation of phenolic compounds. These phenolics may play a role in the protection of potato tubers against S. scabiei.

Construction and yield optimization of a cinnamylamine biosynthesis route in Escherichia coli

Background

With the development of metabolic engineering and synthetic biology, the biosynthesis of aromatic compounds has attracted much attention. Cinnamylamine is an aromatic compound derived from l-phenylalanine, which is used in the synthesis of biologically active molecules, including drugs, and energetic materials. Cinnamylamine has been mainly synthesized by chemical methods to date, and few reports have focused on the biosynthesis of cinnamylamine. Therefore, it is desirable to establish an efficient biosynthesis method for cinnamylamine.

Results

The ω-aminotransferase Cv-ωTA from Chromobacterium violaceum has been demonstrated to have high enzyme activity in the conversion of cinnamaldehyde to cinnamylamine. To prevent the preferable conversion of cinnamaldehyde to cinnamyl alcohol in wild-type Escherichia coli, the E. coli MG1655 strain with reduced aromatic aldehyde reduction (RARE) in which six aldehyde ketone reductase and alcohol dehydrogenase genes have been knocked out was employed. Then, the carboxylic acid reductase from Neurospora crassa (NcCAR) and phosphopantetheinyl transferase (PPTase) from E. coli were screened for a high conversion rate of cinnamic acid to cinnamaldehyde. To shift the equilibrium of the reaction toward cinnamylamine, saturation mutagenesis of Cv-ωTA at key amino acid residues was performed, and Cv-ωTA Y168G had the highest conversion rate with 88.56 mg/L cinnamylamine obtained after 4 h of fermentation. Finally, by optimizing the substrates and the supply of the cofactors, PLP and NADPH, in the fermentation, the yield of cinnamylamine in engineered E. coli reached 523.15 mg/L.

Conclusion

We achieved the first biosynthesis of cinnamylamine using cinnamic acid as the precursor in E. coli using a combinatorial metabolic engineering strategy. This study provides a reference for the biosynthesis of other amine compounds and lays a foundation for the de novo synthesis of cinnamylamine.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02199-7.

Plant-microbe hybrid synthesis provides new insights for the efficient use of Macleaya cordata

Sanguinarine and chelerytrine have antibacterial and anti-inflammatory effects and is the main active ingredients of growth promoters in animals. Currently, Sanguinarine and chelerytrine were extracted from the capsules of the medicinal plant Macleaya cordata. However, the biomass of M. cordata nonmedicinal parts (leaves) accounted for a large proportion and contained a rich presentation of protopine and allocryptopine which are the precursor compounds of sanguinarine and chelerytrine. The aim of this study was to develop a new method for producing sanguinarine and chelerytrine through yeast transformation of protopine and allocryptopine in M. cordata leaves. First, we isolated different genes from Papaver somniferum (PsP6H, PsCPR, PsDBOX), Eschscholtzia californica (EcP6H), Cucumis sativus (CuCPR), Arabidopsis thaliana (AtCPR) and M. cordata (Mc11229, Mc11218, Mc6408, Mc6407, Mc19967, Mc13802). Additionally, some of the gene sequences were codon optimized. Then, we transformed these genes into yeast cells to compare the catalytic efficiency. Second, we used the most efficient strains to biotransform the leaves of M. cordata. Finally, we obtained 85.415 ± 11.887 ng mL^-1 sanguinarine and 4.288 ± 1.395 ng mL^-1 chelerytrine, which was more than 2-3 times the content in leaves of M. cordata. Overall, we using the nonmedicinal parts of M. cordata and successfully obtained sanguinarine and chelerytrine by the plant-microbial hybrid synthesis method.

Efficient whole-cell oxidation of α,β-unsaturated alcohols to α,β-unsaturated aldehydes through the cascade biocatalysis of alcohol dehydrogenase, NADPH oxidase and hemoglobin

Background

α,β-Unsaturated aldehydes are widely used in the organic synthesis of fine chemicals for application in products such as flavoring agents, fragrances and pharmaceuticals. In the selective oxidation of α,β-unsaturated alcohols to the corresponding α,β-unsaturated aldehydes, it remains challenging to overcome poor selectivity, overoxidation and a low atom efficiency in chemical routes.

Results

An E. coli strain coexpressing the NADP⁺-specific alcohol dehydrogenase YsADH and the oxygen-dependent NADPH oxidase TkNOX was constructed; these components enabled the NADP⁺ regeneration and catalyzed the oxidation of 100 mM 3-methyl-2-buten-1-ol to 3-methyl-2-butenal with a yield of 21.3%. The oxygen supply was strengthened by introducing the hemoglobin protein VsHGB into recombinant E. coli cells and replacing the atmosphere of the reactor with pure oxygen, which increased the yield to 51.3%. To further improve catalytic performance, the E. coli cells expressing the multifunctional fusion enzyme YsADH-(GSG)-TkNOX-(GSG)-VsHGB were generated, which completely converted 250 mM 3-methyl-2-buten-1-ol to 3-methyl-2-butenal after 8 h of whole-cell oxidation. The reaction conditions for the cascade biocatalysis were optimized, in which supplementation with 0.2 mM FAD and 0.4 mM NADP⁺ was essential for maintaining high catalytic activity. Finally, the established whole-cell system could serve as a platform for the synthesis of valuable α,β-unsaturated aldehydes through the selective oxidation of various α,β-unsaturated alcohols.

Conclusions

The construction of a strain expressing the fusion enzyme YsADH-(GSG)-TkNOX-(GSG)-VsHGB achieved efficient NADP⁺ regeneration and the selective oxidation of various α,β-unsaturated alcohols to the corresponding α,β-unsaturated aldehydes. Among the available redox enzymes, the fusion enzyme YsADH-(GSG)-TkNOX-(GSG)-VsHGB has become the most recent successful example to improve catalytic performance in comparison with its separate components.

Bioaldehydes and beyond: Expanding the realm of bioderived chemicals using biogenic aldehydes as platforms

Biofuels and biochemicals derived from renewable resources are sconsidered as potential solutions for the energy crisis and associated environmental problems that human beings are facing today. However, so far the available types of bioderived chemicals are rather limited, and production efficiency is generally low. Expanding the realm of bioderived chemicals and relevant derivatives can help motivate the development of bioenergy and the general bioeconomy. Aldehydes, possessing unique reactivity, hold great promise as platform chemicals for producing a large portfolio of bioproducts. In this review, we focus on production of aldehydes from renewable bioresources and derivatization of aldehydes through chemocatalysis, biocatalysis, or de novo biosynthesis. Perspectives on combining protein engineering and cascade reactions for advanced aldehyde derivatization are also provided.

Three steps in one pot: biosynthesis of 4-hydroxycinnamyl alcohols using immobilized whole cells of two genetically engineered Escherichia coli strains

Background

4-Hydroxycinnamyl alcohols are a class of natural plant secondary metabolites that include p-coumaryl alcohol, caffeyl alcohol, coniferyl alcohol and sinapyl alcohol, and have physiological, ecological and biomedical significance. While it is necessary to investigate the biological pathways and economic value of these alcohols, research is hindered because of their limited availability and high cost. Traditionally, these alcohols are obtained by chemical synthesis and plant extraction. However, synthesis by biotransformation with immobilized microorganisms is of great interest because it is environmentally friendly and offers high stability and regenerable cofactors. Therefore, we produced 4-hydroxycinnamyl alcohols using immobilized whole cells of engineered Escherichia coli as the biocatalyst.

Results

In this study, we used the recombinant E. coli strain, M15–4CL1–CCR, expressing the fusion protein 4-coumaric acid: coenzyme A ligase and the cinnamoyl coenzyme A reductase and a recombinant E. coli strain, M15–CAD, expressing cinnamyl alcohol dehydrogenase from Populus tomentosa (P. tomentosa). High performance liquid chromatography and mass spectrometry showed that the immobilized whole cells of the two recombinant E. coli strains could effectively convert the phenylpropanoic acids to their corresponding 4-hydroxycinnamyl alcohols. Further, the optimum buffer pH and the reaction temperature were pH 7.0 and 30 °C. Under these conditions, the molar yield of the p-coumaryl alcohol, the caffeyl alcohol and the coniferyl alcohol was around 58, 24 and 60%, respectively. Moreover, the highly sensitive and selective HPLC–PDA–ESI–MSn method used in this study could be applied to the identification and quantification of these aromatic polymers.

Conclusions

We have developed a dual-cell immobilization system for the production of 4-hydroxycinnamyl alcohols from inexpensive phenylpropanoic acids. This biotransformation method is both simple and environmental-friendly, which is promising for the practical and cost effective synthesis of natural products.Graphical abstract

Expression of Codon-Optimized Plant Glycosyltransferase UGT72B14 in Escherichia coli Enhances Salidroside Production

Salidroside, a plant secondary metabolite in Rhodiola, has been demonstrated to have several adaptogenic properties as a medicinal herb. Due to the limitation of plant source, microbial production of salidroside by expression of plant uridine diphosphate glycosyltransferase (UGT) is promising. However, glycoside production usually remains hampered by poor expression of plant UGTs in microorganisms. Herein, we achieved salidroside production by expression of Rhodiola UGT72B14 in Escherichia coli (E. coli) and codon optimization was accordingly applied. UGT72B14 expression was optimized by changing 278 nucleotides and decreasing the G+C content to 51.05% without altering the amino acid sequence. The effect of codon optimization on UGT72B14 catalysis for salidroside production was assessed both in vitro and in vivo. In vitro, salidroside production by codon-optimized UGT72B14 is enhanced because of a significantly improved protein yield (increased by 4.8-fold) and an equivalently high activity as demonstrated by similar kinetic parameters (K_M and V_max), compared to that by wild-type protein. In vivo, both batch and fed-batch cultivation using the codon-optimized gene resulted in a significant increase in salidroside production, which was up to 6.7 mg/L increasing 3.2-fold over the wild-type UGT72B14.