Table 2.

Crocin biosynthesis by metabolic engineering.

Species	Transgene	Operational methods	Products	Yield	Refs
Escherichia coli	GjUGT94E13, GjUGT74F8	Co-transformation of expression vectors	Crocins	60.81 ± 1.0 mg/L	[44]
Escherichia coli	CsCCD2, NcALD8, BsYjiC, BsYdhE, BsYojK	Integrated genes into the E. coli chromosome by multigene vector and electroporation- transformation	Crocins		[39]
Saccharomyces cerevisiae	PsCrtZ, CCD2, SsALD	Transformation in steps via the lithium acetate method and integrated genes into chromosome	Crocetin	6.28 mg /L	[62]
Chlorella vulgaris	HpCrtRB, CsZCD1	Agrobacterium-mediated transformation and integrated genes into chromosome	Crocetin		[61]
Nicotiana benthamiana	CsCCD2L, BdCCD4.1, BdCCD4.3, PaCrtB, CsBCH2,	Virus vectors transient expression in leaves by Agrobacterium-mediated co-trasformation	Crocins and Picrocrocin (derived from 3-OH-β-cyclocitral, the side product of zeaxanthin cleavage)	2.2 ± 0.2 mg/g crocins and 8.2 ± 2.93 mg/g picrocrocin	[63]

Note: NcALD8, Neurospora crassa aldehyde dehydrogenases gene; BsYjiC, BsYdhE and BsYojK, Bacillus subtilis glycosyltransferase genes; PsCrtZ Pantoea stewartii β-carotene hydroxylase gene; SsALD Synechocystis sp. aldehyde dehydrogenase gene; HpCrtRB, Haematococcus pluvialis β-carotene hydroxylases gene; CsZCD1, Crocus sativus 7, 8 (7′, 8′) -zeaxanthin cleavage dioxygenase gene; PaCrtB, Pantoea ananatis phytoene synthase gene.