Current aspects of auxin biosynthesis in plants

Figures & data

Fig. 1. A schematic model of auxin biosynthesis, inactivation, transport, and signal transduction in plants.

Notes: GH3: IAA-amino acid conjugate synthase, UGT: UDP-glucosyltransferase, IAMT: IAA-methyltransferase, and DAO: dioxygenase for auxin oxidation.

Fig. 2. A schematic model of the IAA biosynthetic pathways and secondary metabolic pathways in Arabidopsis.

Notes: The common Trp biosynthesis and IPA pathways are shown in blue, the IAOx pathway in Arabidopsis is shown in green, the IAM pathway is shown in purple, the TAM pathway is shown in gray, the Trp-independent pathway is shown in red, and secondary metabolite pathways in Arabidopsis are shown in brown. The IPA pathway that is highly conserved in land plants is enclosed in the box. Characterized enzyme reaction steps are in bold typeface. Enzyme reaction steps remaining to be clarified are shown by dashed arrows. TRP3/TSA1: Trp synthase α-subunit and TRP2/TSB1: Trp synthase β-subunit.

Table 1. Current view of IAA biosynthesis pathways in Arabidopsis.

Pathways	Genes	Enzymes	Substrate/product	Reduction of metabolites in knockout mutants	Physiological roles	Orthologs in nonvascular plants
IPA pathway	TAAs	Tryptophan aminotransferase	Trp/IPA	yes	yes	yes
	YUCs	Flavin-containing monooxygenase	IPA/IAA	yes	yes	yes
IAOx pathway	CYP79Bs	Cytochrome P450 monooxygenase	Trp/IAOx	yes	yes	–
	NITs	Nitrilase	IAN/IAA	–	–	–
IAM pathway	AMI1	Amidase	IAM/IAA	–	–	–
TAM pathway	AAOs	Aldehyde oxidase	IAAld/IAA	–	–	–
Trp-independent pathway	INS	Indole synthase	IGP/IND	yes	yes	–

Note: Dashes indicate the data were not observed or reported.

Fig. 3. IAA biosynthesis gene knockout mutants in Arabidopsis.

Notes: (A) Seven-week-old seedlings of yuc multiple mutants and taa double mutants. Bars are 3 cm. (B) Two-week-old seedlings of WT, yuc1D and sur1 and sur2. Bars are 1 cm. (C) Four-week-old seedlings of cyp79b2 cyp79b3 double mutants. Bars are 3 cm.

Fig. 4. TAA1 and YUC expression patterns in pTIR2:GUS and pYUCs:GUS lines.

Notes: (A) Expression patterns of TAA1, YUC1-YUC5, YUC8, and YUC9 in Arabidopsis seedlings (Refs. 36, 42, 43). (B) YUC2, YUC3, and YUC4 expressions in pYUC2:GUS, pYUC3:GUS, and pYUC4:GUS, respectively (Refs. 42 and 43).

Yamada M, Greenham K, Prigge MJ, et al. The TRANSPORT INHIBITOR RESPONSE2 gene is required for auxin synthesis and diverse aspects of plant development. Plant Physiol. 2009;151:168–179.10.1104/pp.109.138859

 PubMed Web of Science ®Google Scholar

Cheng Y, Dai X, Zhao Y. Auxin biosynthesis by the YUCCA flavin monooxygenases controls the formation of floral organs and vascular tissues in Arabidopsis. Genes Dev. 2006;20:1790–1799.10.1101/gad.1415106

 PubMed Web of Science ®Google Scholar

Chen Q, Dai X, De-Paoli H, et al. Auxin overproduction in shoots cannot rescue auxin deficiencies in Arabidopsis roots. Plant Cell Physiol. 2014;55:1072–1079.10.1093/pcp/pcu039

 PubMed Web of Science ®Google Scholar