Rationally optimized generation of integrated Escherichia coli with stable and high yield lycopene biosynthesis from heterologous mevalonate(MVA)and lycopene expression pathways

The stability and high productivity of heterogeneous terpenoid production in Escherichia coli expression system is one of the most key issues for its large scale industrialization.In the current study on taking lycopene biosynthesis as an example,an integrated Escherichia coli system has been generated successfully,which resulted into stable and high lycopene production.In this process,two modules of mevalonate(MVA)pathway and one module of lycopene expression pathway were completely integrated in the chromosome.Firstly,the copy number and integrated position of three modules of heterologous pathways were rationally optimized.Later,a strain DH416 equipped with heterogeneous expression pathways through chromosomal integration was efficiently derived from parental strain DH411.The evolving DH416 strain efficiently produced the lycopene level of 1.22 g/L(49.9 mg/g DCW)in a 5 L fermenter with mean productivity of 61.0 mg/L/h.Additionally,the integrated strain showed more genetic stability than the plasmid systems after successive 21st passage.

An update on the function and regulation of methylerythritol phosphate and mevalonate pathways and their evolutionary dynamics

Isoprenoids are among the largest and most chemically diverse classes of organic compounds in nature and are involved in the processes of photosynthesis, respiration, growth, development,and plant responses to stress. The basic building block units for isoprenoid synthesis-isopentenyl diphosphate and its isomer dimethylallyl diphosphate-are generated by the mevalonate (MVA) and methylerythritol phosphate(MEP) pathways. Here, we summarize recent advances on the roles of the MEP and MVA pathways in plant growth, development and stress responses, and attempt to define the underlying gene networks that orchestrate the MEP and MVA pathways in response to developmental or environmental cues.Through phylogenomic analysis, we also provide a new perspective on the evolution of the plant isoprenoid pathway. We conclude that the presence of the MVA pathway in plants may be associated with the transition from aquatic to subaerial and terrestrial environments, as lineages for its core components are absent in green algae. The emergence of the MVA pathway has acted as a key evolutionary event in plants that facilitated land colonization and subsequent embryo development, as well as adaptation to new and varied environments.

Arabidopsis Squalene Epoxidase 3 （SQE3） Complements SQE1 and Is Important for Embryo Development and Bulk Squalene Epoxidase Activity

The existence of multigenic families in the mevalonate pathway suggests divergent functional roles for pathway components involved in the biosynthesis of plant sterols. Squalene epoxidases （SQEs） are key components of this pathway, and Squalene Epoxidase 1 （SQE1） has been identified as a fundamental enzyme in this biosynthetic step. In the present work, we extended the characterization of the remaining SQE family members, phylogenetically resolving between true SQEs and a subfamily of SQE-like proteins that is exclusive to Brassicaceae. Functional characterization of true SQE family members, Squalene Epox- idase 2 （SQE2） and Squalene Epoxidase 3 （SQE3）, indicates that SQE3, but not SQE2, contributes to the bulk SQE activity in Arabidopsis, with sqe3-1 mutants accumulating squalene and displaying sensitivity to ter- binafine. We genetically demonstrated that SQE3 seems to play a particularly significant role in embryo development. Also, SQE1 and SQE3 both localize in the endoplasmic reticulum, and SQE3 can functionally complement SQEI. Thus, SQE1 and SQE3 seem to be two functionally unequal redundant genes in the pro- motion of plant SQE activity in Arabidopsis.