HO
O
MEP
Pathway
O
P
OH
H
OH
DXR
OP
OP
O
OH
OH
O
HO
OH
O
O
MCT
OP
P
OH
O
OP
NH2
O
N
P
O
OH
OH
HO
O
CMK
N
O
OH
OH
2-C-Methyl-D-eryth
ritol 4-phosphate
1-Deoxy-D-xylulose
5-phosphate
D-Glyceraldehyde
3-phosphate
OH
OH
DXS
OH
4-(Cytidine 5'-diphospho)
-2-C-methyl-D-erythritol
O
P
O
N
P
OH
O
HDS
O
OH
HO
O
O
MDS
N
O
OH
OH
O
NH2
O
P
OH
1-Hydroxy-2-methyl2-butenyl 4-diphosphate
2-C-Methyl-D-erythritol
2,4-cyclodiphosphate
2-Phospho-4-(cytidine 5'-diphospho)
-2-C-methyl-D-erythritol
PP
OH
OH
HDR
O
HMGS
MVA
Pathway
OH
O
S-CoA
HMGR
O
HO
O
OH
MK
O
PMK
HO
HO
O
PP
OH
CH 2
MPD
HO
OH
Mevalonic acid
3-Hydroxy-3-methylglutaryl-CoA
O
OH
O
S-CoA
Acetyl-CoA
AACT
O
O
IDI
O
PP
O
PP
PP
Terpenoid backbone
Dimethylallyl diphosphate
Isopentenyl diphosphate
(R)-5-Diphosphomevalonate
(R)-5-Phosphomevalonate
S-CoA
GPPS
Acetoacetyl-CoA
PP
O
H
H
SQS1
O
O
PP
PP
FDPS1
Farnesyl diphosphate
Presqualene diphosphate
Geranyl diphosphate
SQS1
Squalene
SMO
CAS1
O
(S)-Squalene-2,3-epoxide
CH2
CH2
H
H
SMT1
CH 2
H
H
CH 2
H
H
H
CYP51G1
CPI1
H
H
CH2
H
FK
H
HO
HO
H
HO
HO
H
H
Cycloartenol
HO
HO
H
Cycloeucalenol
24-Methylenecycloartanol
H
H
4¦Á -Methylf ecosterol
¦Ä8,14 -Sterol
Obtusifoliol
HYD1
Steroids
HC
HC
HC
DWF5
HO
STE1
HO
Isofucosterol
CH2
HC
CH2
SMT2
HO
HO
HO
¦Ä 7-Avenasterol
5-Dehydroavenasterol
HO
Episterol
24-Methylene lophenol
24-Ethylidene lophenol
CH 3
STE1
DWF1
CH2
H
H
CH2
CH3
CYP710A
HO
HO
HO
SCCE
SCCE
Stigmasterol
Sitosterol
DWF5
DWF1
HO
HO
24-Methylenecholesterol
Campesterol
5-Dehydroepisterol
O
H
H
H
HO
Pregnenolone
3¦Â-HSD
3¦Â-HSD
H
3-KSI
H
5¦Â-POR
H
H
H
H
O
O
O
Isoprogesterone
3¦Â-HS-5¦Â-OR
H
Progesterone
O
O
O
O
O
H
mono-oxygenases?
H
H
H
HO
H
5¦Â-pregnan-3,20-dione
H
H
H
HO
H
OH
H
3¦Â,14¦Â-dihydroxy-5¦Â-pregnan-20-one
3¦Â-hydroxy-5¦Â-pregnan-20-one
( pregnanolone )
pregnane hydroxylases ?
O
O
O
O
O
O
O
O
O
O
H
H
Glc-Dig-Dig-Dig-O
OH
GT/UGT
H
OH
H
Dig-Dig-Dig-O
H
OH
H
OH
H
HO
H
H
Gitoxigenin
O
H
OH
HO
HO
H
Gitoxin
Purpureaglycoside B
H
Digitoxigenin
O
HOH2 C
OH
H
H
OH
OH
O
O
Dp21MaT
H
HO
H
21-O-malonyl 5¦Â-pregnan-3¦Â,14¦Â-dihydroxy-20-one
O
H
OH
OH
H
3¦Â,14¦Â, 21-trihydroxy-5¦Â -pregnan-20-one
D12H
HO
H
H
HO
O
O
H
OH
O
Digoxigenin
O
HO
H
H
H
Dig-Dig-Dig- O
OH
H
D12H
Dig-Dig-Dig- O
H
H
Digoxin
OH
Digitoxin
GT/UGT
GT/UGT
CGH I
O
O
CGH I
O
O
OH
D12H
H
H
Glc-Dig-Dig-Dig- O
H
OH
H
Glc-Dig-Dig-Dig- O
H
Desacetyl-lanatoside C
OH
H
Purpureaglycoside A
Additional file 8. The putative biosynthetic pathway of cardiac glycosides in
Digitalis Purpurea.
The pathway roughly comprises terpenoid backbone biosynthesis, steroid biosynthesis and cardenolide
biosynthesis
three
stages.
The
enzymes
with
corresponding
unigenes
are
framed.
Abbreviation:
DXS,1-deoxy-D-xylulose-5-phosphate synthase; DXR,1-deoxy-D-xylulose-5-phosphate reductoisomerase; MCT,
2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase; CMK, 4-diphosphocytidyl-2-C-methyl-D-erythritol
kinase; MDS,2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase; HDS,4-hydroxy-3-methylbut-2-en-1-yl
diphosphate
synthase;
HDR,4-hydroxy-3-methylbut-2-enyl
diphosphate
reductase;
AACT,acetyl-CoA
C-acetyltransferase; HMGS,hydroxymethylglutaryl-CoA synthase; HMGR,hydroxymethylglutaryl-CoA reductase;
MK, mevalonate kinase; PMK, phosphomevalonate kinase; MPD, diphosphomevalonate decarboxylase;
Cardenolides
IDI,isopentenyl-diphosphate delta-isomerase; GGPPS1,geranylgeranyl pyrophosphate synthase 1; FDPS1,farnesyl
diphosphate synthase 1; SQS1,squalene synthase 1; SMO,squalene monooxygenase; CAS1,cycloartenol synthase 1;
SMT1,sterol 24-C-methyltransferase; CPI1,cyclopropyl isomerase; CYP51G1,cytochrome P450, family 51,
subfamily A (sterol 14-demethylase); FK, delta14-sterol reductase; HYD1， cholestenol delta-isomerase; SMT2，
sterol methyltransferase 2; STE1， C-5 sterol desaturase; DWF5， sterol delta7 reductase ; DWF1，delta24-sterol
reductase;
SCCE ， cholesterol
monooxygenase
(side-chain-cleaving);
3βHSD ， 3-beta-hydroxysteroid
dehydrogenase; 3-KSI， △5-3-ketosteroid isomerase; 5βPOR，progesterone 5β-reductase; 3βHS- P5βOR，
3β-hydroxysteroid 5β-oxidoreductase; Dp21MaT，21-hydroxypregnane 21-O-malonyltransferase; D12H，digitoxin
12β-hydroxylase; CGHⅠ，cardenolide 16-O-glucohydrolase; GT，glycosyltransferase/ glucuronosyltransferase;
UGT，UDP- glycosyltransferase/ glucuronosyltransferase.