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.
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) |