Vitamins in Fleshy Fruits - Fruit Ripening: Physiology, Signalling and Genomics - page 133

Glyceraldehyde-3-P + Pyruvate Phosphoenolpyruvate + erythrose-4-P

DAHPS

DXS

1-Deoxy- D -arabino-heptulosonate-7-P

1-Deoxy- D -xylulose-5-P

DHQS

DXR

3-Dehydroquinate

2-C-Methyl- D -erythritol-4-P

DHQ

CMS

3-Dehydroshikimate

-diphospho)-2-C-methyl- D -erythritol-4-P

4-(cytidine 5

SDH

ISPE

Shikimate

-diphospho)-2-C-methyl- D -erythritol-4-P

2-Phospho-4-(cytidine 5

SK

ISPF

Shikimate-3-P

2-C-Methyl- D -erythritol-2,4-cyclodiphosphate

EPSPS

HDS

5-Enolpyruvylshikimate-3-P

1-Hydroxy-2-methyl-2-butenyl-4-diphosphate

CS

HDR

Chorismate Tryptophan

Isopentenyl-2P Dimethylallyl-2P CM Folate

IPI

Prephenate

GGPS GPPS

PAT

Arogenate Phenylalanine

TyrA

PDS Geranyl-2P

Lycopene Geranylgeranyl-2P

Tyrosine

LYCB GGDR

TAT

β -Carotene Phytyl-2P

Hydroxyphenylpyruvate

HPPD

Homogentisate

HPT

HST/HGGT

2-Methyl-6-phytylquinol 2-Methyl-6-geranylgeranylbenzoquinol

Phytyl-2P

MPBQMT

MPBQMT

TC TC

2,3-Dimethyl-6-geranylgeranylbenzoquinol

PK 2,3-Dimethyl-5-phytylquinol

TC TC

Phytol

-Tocopherol -Tocopherol -Tocotrienol -Tocotrienol

γ δ γ δ

CHL

TMT TMT TMT TMT

Chlorophyll a α -Tocopherol β -Tocopherol α -Tocotrienol β -Tocotrienol

Fig. 8.2. Biosynthetic routes of vitamin E reactions in plants displaying the methylerythritol 4-phosphate
(MEP), shikimate kinase (SK) and tocopherol core pathways as well as the VTE-related pathways
(carotenoid, chlorophyll, tryptophan, phenylalanine and folate).The corresponding enzymes are: DXS,
deoxy- D -xylulose-5- phosphate synthase; DXR, 2-C-methyl- D -erythritol 4-phosphate synthase; CMS,
2-C-methyl- D -erythritol 4-phosphate cytidylyltransferase; ISPE, 4-(cytidine 5 c -diphospho)-2-C-methyl- D -
erythritol kinase; ISPF, 2-C-methyl- D -erythritol 2,4-cyclodiphosphate synthase; HDS, 4-hydroxy-3-
methylbut-2-enyl diphosphate synthase; HDR, 4-hydroxy-3-methylbut-2-enyl diphosphate reductase; IPI,
isopentenyl diphosphate isomerase; GPPS, geranyl pyrophosphate synthase; GGPS, geranylgeranyl
pyrophosphate synthase; GGDR, geranylgeranyl reductase; DAHPS, 3-deoxy- D -arabino-heptulosonate-7-
phosphate synthase; DHQS, 3-dehydroquinate synthase; SDH, shikimate dehydrogenase; DHQ,
3-dehydroquinate dehydratase; EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase; CS, chorismate
synthase; CM, chorismate mutase; PAT, prephenate aminotransferase; TyrA, arogenate dehydrogenase; TAT,
tyrosine aminotransferase; HPPD, 4-hydroxyphenylpyruvate dioxygenase; HTS/HGGT, homogentisate
solanesyl transferase/homogentisate geranylgeranyl transferase; HPT (VTE2), homogentisate phytyl
transferase; MPBQMT(VTE3), 2-methyl-6-phytyl-1,4-benzoquinone methyltransferase; TC (VTE1),
tocopherol cyclase; J -TMT (VTE4), J -tocopherol methyl transferase; PK, phytol kinase; CHL, chlorophyllase;
LYCB, lycopene E -cyclase. P, phosphate; 2P, diphosphate.

(see Part I). These include the transition
from chloroplasts, which are present in the
green tissues from developing tomato fruit
until the onset of ripening, to carotenoid-
accumulating chromoplasts in the
coloured fruit. Carotenoids present in
chloroplasts are mostly the carotene-
derived xanthophylls, associated with
photosynthesis, whilst in chromoplasts the
acyclic carotenoids (phytoene, phyto-

fl uene, E -carotene, neurosporene and
lycopene) accumulate. In tomato, the
transcriptional upregulation of carotenoid
biosynthesis genes is the major regulatory
mechanism that takes place in fruit (Fraser
et al. , 2009). There is a massive increase in
transcripts for PSY and PDS, concomitant
with a disappearance of the transcripts for
the lycopene cyclases encoded by LYCB
and LYCE . In addition, an alternative set of