two branches of the aspartate pathway use initially a common substrate: O-phosphohomoserine (OPHS). It is now clearly established that in the methionine branch of the
aspartate pathway all enzymes are present in the chloroplast. Therefore, chloroplasts
are autonomous for de novo Met biosynthesis (Mills et al. 1980; Ravanel et al. 2004).
1
*
-KG
AdoMet
*
Glycerate-3-P
PEP
aspartate
asparagine
glutamate
Chorismate
serine
glycine
homoserine
valine
threonine
proline
methionine
4-homoserine-4P
leucine
Acetyl-CoA
citrate
-ketoglutarate
malate
oxaloacetate
succinate
fumarate
Pyruvate
-alanine
-alanine
2-keto
isovalerate
tyrosine
DHAP
glutamine
arginine
*
Glucose
Fructose 1,6-biphosphate
2
anthranilate
PAA
phenylalanine
prephenate
4
7
8
9
AICAR
de novo Purine
biosynthesis
histidine
IGP
IAP
histidinol-P
*
14
6
6
ethylene
*
11
polyamines
5
serine
3
*
1?
imidazol-5yl-pyruvate
GABA
12
lysine
Isoleucine
Pentose phosphate
pathway
5’-PRFAR
PRPP
6
5-phosphoribosyl anthranilate
*
1
tryptophane
IAA
PP i
glutamate
13
+ ATP
*
10
arogenate
8
*
dcAdoMet
PEPCK
β
α
α
α
Fig. 1 Simplified overview of amino acid biosynthesis in plants. Asterisk indicates aminotransferases targeted by AVG and number represents PLP-dependent aminotransferases in the different
biosynthetic pathways: 1, tryptophan aminotransferase of Arabidopsis (TAA); 2, 3-phosphoserine
aminotransferase (PSAT) and ala-hydroxypyruvate aminotransferase (HA-AT); 3, alaninehydroxypyruvate aminotransferase (AH-AT); 4, Alanine aminotransferase (AlaAT); 5, β-alaninepyruvate aminotransferase (BAPAT); 6, branched-chain aminotransferase (BCAT); 7 and 8,
eukaryotic aspartate aminotransferase (ET-AAT) and prokaryotic type aspartate/prephenate aminotransferase (PT-AAT/PAT); 9, asparagine synthase (ASN); 10, cystathionine β-lyase (CBL); 11,
1-aminocyclopropane-1-carboxylate synthase (ACS); 12, glutamate decarboxylase (GAD); 13,
Gaba transaminases using either α-ketoglutarate (GABA-TK) or pyruvate (GABA-TP); 14,
histidinol-phosphate aminotransferase (HPA). Abbreviations used for metabolites are: 5
0 -PRFAR
phosphoribosyl
formimino-5-aminoimidazole0 -carboxamide
ribonucleotide,
IGP
imidazoleglycerolphosphate, IAP imidazoleacetolphosphate, AICAR 5-aminoimidazole-4carboxamideribonucleotide, α-KG α-ketoglutarate, IAA indole-3-acetic acid, PAA phenylacetic
acid, SAM S-Adenosylmethionine, PEPCK phosphoenolpyruvate carboxykinase. Green boxes
indicate plastidic location of enzymes. ? indicates putative degradation pathway of histidine by
tryptophan aminotransferase according to Brunke et al. (2014) in C. glabrata and S. cerevisiae
(adapted from Coruzzi and Last 2000)
From Aspartate to Ethylene: Central Role of N, C, and S Shuttles by. . .
257
aspartate pathway all enzymes are present in the chloroplast. Therefore, chloroplasts
are autonomous for de novo Met biosynthesis (Mills et al. 1980; Ravanel et al. 2004).
1
*
-KG
AdoMet
*
Glycerate-3-P
PEP
aspartate
asparagine
glutamate
Chorismate
serine
glycine
homoserine
valine
threonine
proline
methionine
4-homoserine-4P
leucine
Acetyl-CoA
citrate
-ketoglutarate
malate
oxaloacetate
succinate
fumarate
Pyruvate
-alanine
-alanine
2-keto
isovalerate
tyrosine
DHAP
glutamine
arginine
*
Glucose
Fructose 1,6-biphosphate
2
anthranilate
PAA
phenylalanine
prephenate
4
7
8
9
AICAR
de novo Purine
biosynthesis
histidine
IGP
IAP
histidinol-P
*
14
6
6
ethylene
*
11
polyamines
5
serine
3
*
1?
imidazol-5yl-pyruvate
GABA
12
lysine
Isoleucine
Pentose phosphate
pathway
5’-PRFAR
PRPP
6
5-phosphoribosyl anthranilate
*
1
tryptophane
IAA
PP i
glutamate
13
+ ATP
*
10
arogenate
8
*
dcAdoMet
PEPCK
β
α
α
α
Fig. 1 Simplified overview of amino acid biosynthesis in plants. Asterisk indicates aminotransferases targeted by AVG and number represents PLP-dependent aminotransferases in the different
biosynthetic pathways: 1, tryptophan aminotransferase of Arabidopsis (TAA); 2, 3-phosphoserine
aminotransferase (PSAT) and ala-hydroxypyruvate aminotransferase (HA-AT); 3, alaninehydroxypyruvate aminotransferase (AH-AT); 4, Alanine aminotransferase (AlaAT); 5, β-alaninepyruvate aminotransferase (BAPAT); 6, branched-chain aminotransferase (BCAT); 7 and 8,
eukaryotic aspartate aminotransferase (ET-AAT) and prokaryotic type aspartate/prephenate aminotransferase (PT-AAT/PAT); 9, asparagine synthase (ASN); 10, cystathionine β-lyase (CBL); 11,
1-aminocyclopropane-1-carboxylate synthase (ACS); 12, glutamate decarboxylase (GAD); 13,
Gaba transaminases using either α-ketoglutarate (GABA-TK) or pyruvate (GABA-TP); 14,
histidinol-phosphate aminotransferase (HPA). Abbreviations used for metabolites are: 5
0 -PRFAR
phosphoribosyl
formimino-5-aminoimidazole0 -carboxamide
ribonucleotide,
IGP
imidazoleglycerolphosphate, IAP imidazoleacetolphosphate, AICAR 5-aminoimidazole-4carboxamideribonucleotide, α-KG α-ketoglutarate, IAA indole-3-acetic acid, PAA phenylacetic
acid, SAM S-Adenosylmethionine, PEPCK phosphoenolpyruvate carboxykinase. Green boxes
indicate plastidic location of enzymes. ? indicates putative degradation pathway of histidine by
tryptophan aminotransferase according to Brunke et al. (2014) in C. glabrata and S. cerevisiae
(adapted from Coruzzi and Last 2000)
From Aspartate to Ethylene: Central Role of N, C, and S Shuttles by. . .
257