Auxin Biosynthesis and Regulation in Plant Development

Auxin, principally indole-3-acetic acid (IAA), orchestrates virtually every phase of plant growth and morphogenesis by forming concentration gradients that guide cell division, elongation and differentiation. Biosynthesis of IAA occurs via multiple tryptophan-dependent pathways, the most thoroughly characterised being the sequential action of tryptophan aminotransferases (TAA/TAR) and YUCCA flavin monooxygenases, which convert tryptophan to indole-3-pyruvate and thence to IAA. Spatial and temporal control of these enzymatic steps underpins the local generation of auxin maxima in meristems, primordia and root apices. Beyond synthesis, homeostatic regulation is achieved by reversible conjugation of IAA to amino acids or sugars, carried out by members of the GH3 and UGT families, and by oxidative inactivation via dedicated dioxygenases. Auxin levels are further refined through polar transport mediated by PIN and AUX/LAX transporters, creating directional fluxes that integrate with biosynthetic and inactivation processes. Together these layers of regulation enable plants to adapt developmental programmes to environmental cues, control organ patterning, maintain stem cell niches and modulate stress responses. Understanding this dynamic network holds promise for targeted manipulation of plant architecture, yield enhancement and resilience to abiotic challenge.

Research from Nature Portfolio

Recent studies have elucidated the principal oxidative inactivation pathway for IAA, revealing a tightly coupled GH3–ILR1–DAO cascade. GH3 amido-synthetases first conjugate IAA to amino acids, generating storage forms such as IAA-Asp and IAA-Glu. These conjugates can be remobilised by ILR1 family hydrolases, but are also subject to irreversible oxidation by the DAO1 dioxygenase, producing oxIAA-amino acid derivatives that are ultimately hydrolysed to yield inactive oxIAA. This complete biochemical route clarifies long-standing questions about auxin turnover, demonstrates how conjugation and oxidation intersect to fine-tune hormone levels, and highlights new targets for modulating developmental outcomes.

Auxin Biosynthesis and Regulation in Plant Development publication trend

The graph below shows the total number of articles in auxin biosynthesis and regulation in plant development across all publications each year (not limited to Nature Index journals).

Technical terms

Indole-3-acetic acid (IAA): Major form of auxin regulating plant growth and development.

YUCCA (YUC): Family of flavin-containing monooxygenases catalysing a key rate-limiting step in IAA biosynthesis via the indole-3-pyruvate pathway.

GH3: Auxin-conjugating enzymes that attach amino acids to IAA, modulating its activity and storage.

ILR1: IAA-amino acid hydrolases that release free IAA from its conjugated forms.

DAO: Dioxygenase oxidising IAA-amino acid conjugates into inactive forms during auxin inactivation.

Conjugation: Attachment of amino acids or sugars to IAA, leading to temporary storage or inactivation.

Oxidative inactivation: Enzymatic oxidation of auxin or its conjugates, resulting in irreversible hormone deactivation.

References

1. The main oxidative inactivation pathway of the plant hormone auxin. Nature Communications (2021).
2. Al-induced CsUGT84J2 enhances flavonol and auxin accumulation to promote root growth in tea plants. Horticulture Research (2023).
3. The Roles of Auxin Biosynthesis YUCCA Gene Family in Plants. International Journal of Molecular Sciences (2019).
4. Control of Endogenous Auxin Levels in Plant Root Development. International Journal of Molecular Sciences (2017).