Table 6.

Synthetic pathways for polyketide and flavonoid synthesis

Host organism	Engineering steps	Substrate	Product/Outcome		Ref
Saccharomyces cerevisiae	1) Introduction of the Penicillium patulum PKS 6-MSASI gene	YPD (+ glucose)		1.7 g/L (2-fold more than by natural host Penicillium patulum)	[232]
	2) Overexpression of the Bacillus subtilis surfactin P-pantII transferase (Sfp) gene
Saccharomyces cerevisiae	1) Introduction of the Penicillium patulum PKS 6-MSASI gene	galactose minimal medium		> 200 mg/L for strain expressing the PPTaseII from A. nidulans	[231]
	2) Introduction of the surfactin P-pantII transferase gene from Bacillus subtilis (sfp) or from Aspergillus nidulans (npgA)
Saccharomyces cerevisiae BJ5464 (protease deficient)	1) Introduction of pathways for methylmalonyl-coenzyme A production:	YPD (+ glucose) + propionate and propyl-diketide thioester feed		0.5–1 mg/L with propionyl-CoA-dependent route (PCC-pathway)	[215]
	Propionyl-CoA-dependent route:
	+ Salmonella typhimurium propionyl-CoA synthetase
	+ Streptomyces coelicolor propionyl-CoA carboxylase pathway (PCC)
	Propionyl-CoA-independent route
	+ Streptomyces coelicolor malonyl/methylmalonyl-CoA ligase pathway (MatB)
	2) Expression of module 2 from DEBS1III linked to the thioesterase domain (TE) of DEBS3 [243,244]
	3) Co-expression of five tRNA genes E4, R2, L5, Q2 and P2 [245]
Saccharomyces cerevisiae	1) Introduction of the Populus trichocarpa X Populus deltoides (= poplar) cDNAs encoding:	selective, synthetic medium supplemented with glucose and galactose, respectively		~3–10 mg/L triple-expressing strains (PAL2/C4H/CPR2 and PAL4/C4H/CPR2, respectively; with slight advantages for the PAL2 expressing strain)	[233]
	+ Phenylalanine ammonia lyase (isoform PAL2 and PAL4, respectively)	feed with [3H]phenylalanine [14C]cinnamate
	+ Cinnamate 4-hydroxylase (C4H)
	+ Cytochrome P450 reductase (CPR2)
Saccharomyces cerevisiae	1) Introduction of the Helianthus tuberosus C4H Cytochrome P-450 and H. tuberosus NADPH-Cytochrome P-450 reductase	glucose or raffinose addition of L-phenylalanine (1.0 mM)		after 24 h:	[234]
	2) Introduction of the Rhodotorula glutinis ATCC 10788 phenylalanine ammonia-lyase (PAL)	induction with galactose		on glucose: 354 μM (→ 58 mg/L)
				on raffinose: 498 μM (→ 82 mg/L)
Saccharomyces cerevisiae AH22	1) Introduction of the phenylpropanoid pathway:	YPD (+ glucose) and YPL (+ galactose)	S. cerevisiae AH22 with PAL, 4CL and CHS produced ~7 mg/L of naringenin and 0.8 mg/L of pinocembrin		[235]
	- Rhodosporidium toruloides phenylalanine ammonia lyase (PAL)
	- Arabidopsis thaliana 4-coumarate:coenzyme A (CoA) ligase (4CL)
	- Hypericum androsaemum chalcone synthase (CHS)
Saccharomyces cerevisiae YPH499	1) Introduction of the chalcone synthase (CHS) from ripe raspberry (Rubus idaeus) or a variant thereof (CHS L214I-F215L)	YPGal-medium (induction with galactose)		raspberry fruit: 1–4 mg/kg	[237]
	2) Introduction of the tobacco 4-coumarate-coenzyme A ligase (4CL)	addition of p-coumaric acid (3 mM)		recombinant E. coli: 5 mg/L	[236]
				recombinant S. cerevisiae: no proper detection of raspberry ketone	[236]
Saccharomyces cerevisiae FY23	1) Introduction of the coenzyme-A ligase 4CL216 gene from hybrid poplar under the control of the yeast ADH2 gene promoter and terminator (→ CAL1) and	SCDL-medium (0.67% yeast nitrogen base, 0.8% glucose and required growth factors) with 10 mg/L p-coumaric acid	recombinant S. cerevisiae: ~1.5 μg/L		[238]
	2) the resveratrol synthase (VST1) from grapevine (Vitis vinifera)
Saccharomyces cerevisiae CEN.PK 113-3b (ura3 his3)	1) Introduction of the 4-coumarate: coenzyme A (CoA) ligase (4CL2 gene – GenBank accession no. U50846) from Nicotiana tabacum cv. Samsun	50 mL yeast nitrogen base medium supplemented with 5 mM p-coumaric acid and 2% galactose to induce gene expression		S. cerevisiae: ~6 mg/L	[239]
	2) Introduction of the STS gene from Vitis vinifera encoding for the stilbene synthase (STS)			recomb. E. coli expressing the same enzymes: ~16 mg/L

^IPKS = polyketide synthase; 6-MSAS = 6-methylsalicylic acid synthase

^IIPPTase = P-pant transferase = 4'-phophopantetheinyl transferase

^IIIDEBS = deoxyerythronolide B synthase from Saccharopolyspora erythraea, a typical 'modular' polyketide synthase.