Auxin Transport Mechanisms in Plant Development

Auxin, principally indole-3-acetic acid, orchestrates a vast array of developmental processes by forming concentration gradients within tissues. These gradients arise through carrier-mediated polar auxin transport, which depends on the asymmetric localisation of influx and efflux proteins in the plasma membrane. Influx carriers of the AUX1/LAX family import auxin into the cytoplasm, whereas PIN-FORMED (PIN) and ABCB transporters facilitate directional efflux. The dynamic distribution of these carriers is controlled at multiple levels, including transcriptional regulation, post-translational modifications such as phosphorylation and S-acylation, and membrane trafficking. Kinases from the AGC family phosphorylate PIN hydrophilic loops, thereby directing their polar localisation and transport activity. Membrane association of other regulators, exemplified by the D6 PROTEIN KINASE (D6PK), relies on specific lipid modifications that stabilise polarity. Together, these processes generate and refine auxin maxima and minima to determine organ initiation, tropic responses, vascular differentiation and overall developmental timing. Computational models anchored in realistic cellular geometries have recently shown that both efflux and influx carriers are indispensable for producing the root-apex auxin pattern. Moreover, growing evidence highlights how environmental cues modulate carrier cycling and developmental clocks, ensuring adaptive growth.

Research from Nature Portfolio

Recent studies have elucidated how plant developmental timing integrates growth and environmental signals. By employing simplified conceptual models, researchers have delineated mechanisms by which intrinsic timing modules and growth-dependent feedback coordinate cyclical and progressive transitions, such as phase changes in leaves and flowering. These insights reveal that developmental “clocks” in plants are tuned by nutrient availability and light, contrasting with autonomous timekeepers in other organisms.

Progress has also been made in understanding the establishment and maintenance of plasma-membrane polarity for key kinases that activate auxin efflux. Investigations into D6PK have identified a repeated CXX(X)P motif whose cysteines undergo S-acylation to mediate membrane binding. Adjacent serine residues are phosphorylated in a PDK1-dependent manner, modulating D6PK cycling to and from the membrane, its lateral mobility and residence time. This dual lipid-and-phosphate code provides a mechanism for the precise spatial control of kinase localisation and, consequently, of PIN activation and polar auxin fluxes.

Auxin Transport Mechanisms in Plant Development publication trend

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

Technical terms

Auxin: A plant hormone, primarily indole-3-acetic acid, that regulates growth and development through differential distribution.

Polar auxin transport (PAT): Directional cell-to-cell movement of auxin mediated by asymmetrically localised influx and efflux carriers.

PIN-FORMED (PIN) proteins: A family of auxin efflux carriers whose polar localisation dictates the direction of auxin flow.

AUX1/LAX carriers: A family of auxin influx transporters that mediate entry of auxin into cells, contributing to local hormone accumulation.

AGC kinases: A group of serine/threonine protein kinases (including D6PK and PID) that phosphorylate targets to control localisation and activity.

S-acylation: A reversible lipid modification involving attachment of fatty acids to cysteine residues, influencing protein–membrane interactions.

Developmental timing: The regulation of temporal progression of developmental events, often modulated by environmental and growth cues.

References

1. Developmental timing in plants. Nature Communications (2024).
2. D6PK plasma membrane polarity requires a repeated CXX(X)P motif and PDK1-dependent phosphorylation. Nature Plants (2024).
3. Divergence of trafficking and polarization mechanisms for PIN auxin transporters during land plant evolution. Plant Communications (2023).
4. Developmental Roles of AUX1/LAX Auxin Influx Carriers in Plants. Frontiers in Plant Science (2019).
5. Systems Analysis of Auxin Transport in the Arabidopsis Root Apex. The Plant Cell (2014).
6. Phosphorylation of Conserved PIN Motifs Directs Arabidopsis PIN1 Polarity and Auxin Transport. The Plant Cell (2010).
7. Paralogous Radiations of PIN Proteins with Multiple Origins of Noncanonical PIN Structure. Molecular Biology and Evolution (2014).