Hormone Synthetic Pathways and Genes in Arabidopsis: Auxin


Auxins have an aromatic ring and a carboxyl acid side chain, and the most common naturally occurring auxin is indole-3-acetic acid (IAA). Auxin plays a central role in the regulation of plant growth and development. At the cellular level, auxin acts as a signal for division, expansion, and differentiation throughout the plant life cycle. At the level of the whole plant, auxin plays important roles in root formation, apical dominance, the tropic responses, fruit development, and senescence. Despite the importance of IAA, its biosynthesis is the least understood of all the classical plant hormones. Multiple biosynthesis pathways have been proposed: one is dependent on tryptophan (Trp), and the other is Trp-independent. In addition, several pathways are known to exist in the Trp-dependent pathway, including the tryptamine (TAM), indole-3-pyruvic acid (IPyA), and indole-3-acetaldoxime (IAOx) pathways. Each pathway has different proposed enzymes and genes that were identified using molecular or genetic approaches. It is still unclear how each pathway contributes to auxin biosynthesis. The major biosynthesis pathway in Arabidopsis is shown here.

Pathway map of Auxin biosynthesis
[MS PowerPoint: 249KB]

Genes on the pathway

Gene name Locus name Description
YUCCA1 At4g32540 tryptamine monooxygenase
YUCCA2 At4g13260 YUCCA gene
YUCCA3 At1g04610 YUCCA gene
YUCCA4 At5g11320 YUCCA gene
YUCCA5 At5g43890 YUCCA gene
YUCCA6 At5g25620 tryptamine monooxygenase
YUCCA7 At2g33230 YUCCA gene
YUCCA8 At4g28720 YUCCA gene
YUCCA9 At1g04180 YUCCA gene
YUCCA10 At1g48910 YUCCA gene
YUCCA11 At1g21430 YUCCA gene
TAA1/SAV3/WEI8 At1g70560 tryptophan aminotransferase of Arabidopsis 1
TAR1 At1g23320 tryptophan aminotransferase related 1
TAR2 At4g24670 tryptophan aminotransferase related 2
TAR3 At1g34040 tryptophan aminotransferase related 3
TAR4 At1g34060 tryptophan aminotransferase related 4
TSA1/TRP3 At3g54640 tryptophan synthase alpha subunit
TSA1 homolog At4g02610 tryptophan synthase alpha subunit homolog
TSB2/TRP2 At4g27070 tryptophan synthase beta subunit
TSB2 homolog At5g38530 tryptophan synthase beta subunit homolog
TSB2 homolog At5g28237 tryptophan synthase beta subunit homolog
CYP79B2 At4g39950 indole-3-acetaldoxime synthase (P450 monooxygenase)
CYP79B3 At2g22330 indole-3-acetaldoxime synthase (P450 monooxygenase)
AAO1 At5g20960 Arabidopsis aldehyde oxydase 1
NIT1 At3g44310 nitrilase 1
NIT2 At3g44300 nitrilase 2
NIT3 At3g44320 nitrilase 3
NIT4 At5g22300 nitrilase 4
AMI1 At1g08980 indole-3-acetamide amidohydrolase
CYP71A13 At2g30770 indoleacetaldoxime dehydratase
CYP83B1/SUR2 At4g31500 super root2 (P450 monooxygenase)
SUR1 At2g20610 super root 1 (C-S lyase)
RIKEN Plant Hormone Research Network - RIKEN Center for Sustainable Resource Science