Fig. 2

β-Carotene biosynthesis in S. cerevisiae and cell response to β-carotene accumulation. a Schematic overview of the β-carotene biosynthetic pathway in S. cerevisiae. The expression of galactose utilization related genes is mainly controlled by proteins Gal4, Gal3 and Gal80. Gal4 is a transcriptional regulatory protein, which can specifically bind to the promoters of the GAL1, GAL7, GAL10, and GAL2 genes to activate the transcription of the aforementioned genes. Gal80 is the inhibitory protein of Gal4. When yeast cells grow in a culture without galactose, Gal80 can specifically bind to Gal4, preventing the binding of Gal4 protein to the promoter region of GAL genes, thereby inhibiting the expression of GAL genes. When the gene GAL80 is knocked out, the expression of GAL4 is only controlled by the Snf1 regulatory network. After the glucose in the medium is exhausted, the inhibition of GAL4 is relieved, then the GAL genes begin to express and drive the product synthesis. The dashed lines indicate multiple step reactions. MVA pathway mevalonate pathway, IPP isopentenyl pyrophosphate, DMAPP dimethylallyl pyrophosphate, GPP geranyl pyrophosphate, FPP farnesyl pyrophosphate, GGPP geranylgeranyl pyrophosphate, crtEp GGPP synthase, crtYBp encoding bifunctional phytoene synthase and lycopene cyclase, crtIp phytoene desaturase. b Time courses of cell growth, the glucose concentration of β-carotene producing strain YBX-01 and its parental strain YBX-B and β-carotene accumulation of YBX-01. c The comparative proteome analysis between YBX-01 and YBX-B at 36 h. d The comparative transcription levels of plasma membrane ABC transporters between YBX-01 and YBX-B throughout the cell growth period. All data represent the mean ± s.d. of biological triplicates