2.1 Construction of strains and plasmids
All the strains and plasmids in this study are listed in Table S1 and S2. E. coli DH5α was used for plasmid construction and BL21(DE3) was chosen as the host strain. All PCR amplifications were performed by PrimeSTAR Max DNA Polymerase (Vazyme, Nanjing, China). The plasmids which were used to express IUP pathway were constructed on the basis of pSU2718 (chloramphenicol-selectable). Plasmids harboring IUP under control of constitutive promotors were constructed through restriction enzyme digestion and ligation (KpnI , BamHI ). To construct Plasmids harboring IUP under the control of inducible promotors, the DNA fragments and plasmid backbone were amplified by PCR and constructed through Gibson assembly. The constructed plasmid was introduced into DH5α by chemical transformation or electro-transformation and correct transformants were confirmed by colony PCR. Plasmids of IUP and enzymes for lycopene production were introduced to BL21(DE3) through electro-transformation.