ABSTRACT
Genetically engineered plants have varied applications in agriculture for enhancing the values of food and feed.Genetic engineering aims to introduce selected genetic regions with desirable traits into target plants for bothspatial and temporal expressions. Promoters are the key elements responsible for regulating gene expressionsby modulating the transcription factors (TFs) through recognition of RNA polymerases. Based on theirrecognition and expression, RNA polymerases were categorized into RNA pol II and pol III promoters.Promoter activity and specificity are the two prime parameters in regulating the transgene expression. Since theuse of constitutive promoters like Cauliflower mosaic virus (CaMV) 35S may lead to adverse effects on nontarget organisms or ecosystem, inducible/tissue specific promoters and/or the RNA pol III promoters providemyriad opportunities for gene expressions with controlled regulation and with minimum adverse effects.Besides their role in transgene expression, their influence in synthetic biology and genome editing are alsodiscussed. This review provides an update on the importance, current prospects, and insight into the advantagesand disadvantages of promoters reported thus far would help to utilize them in the endeavour to developnutritionally and agronomically improved transgenic crops for commercialization.
ABSTRACT
cis, cis-muconic acid (MA) is an important platform chemical. Now, majority of reported engineered strains are genetically instable, the exogenous genes are expressed under the control of expensive inducer and the components of their fermentation medium are complex, thus large-scale microbial production of MA is limited due to the lack of suitable strains. Hence, it is still necessary to construct novel high-performance strain that is genetically stable, no induction and grows in simple inorganic fermentation medium. In this study, after 3 exogenous genes (aroZ, aroY, catA) for biosynthesis of MA were integrated into previously constructed 3-hydroshikimate producing Escherichia coli WJ060 strain and combinatorially regulated with 3 constitutive promoters with different strengths, 27 engineered strains were constructed. The best engineered strain, E. coli MA30 could produce 1.7 g/L MA in the simple inorganic fermentation medium without induction. To further enhance the production capacity of MA, the mutant library of E. coli MA30 was constructed by genome replication engineering and screened via high-throughput assay. After two-round screening, the new strain, E. coli MA30-G2 with improved production of MA was obtained, and the titer of MA increased more than 8%. Under the condition of 5 L fed-batch fermentation, E. coli MA30-G2 could produce about 11.5 g/L MA. Combinatorial regulation and high-throughput screening provide important reference to microbial production of other bio-based chemicals.