phot1 inhibition of ABCB19 primes lateral auxin fluxes in the shoot apex required for phototropism.

It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots.

Mutation of the membrane-associated M1 protease APM1 results in distinct embryonic and seedling developmental defects in Arabidopsis.

Aminopeptidase M1 (APM1), a single copy gene in Arabidopsis thaliana, encodes a metallopeptidase originally identified via its affinity for, and hydrolysis of, the auxin transport inhibitor 1-naphthylphthalamic acid (NPA). Mutations in this gene result in haploinsufficiency. Loss-of-function mutants show irregular, uncoordinated cell divisions throughout embryogenesis, affecting the shape and number of cotyledons and the hypophysis, and is seedling lethal at 5 d after germination due to root growth arrest.

Post-transcriptional regulation of auxin transport proteins: cellular trafficking, protein phosphorylation, protein maturation, ubiquitination, and membrane composition.

Auxin concentration gradients, established by polar transport of auxin, are essential for the establishment and maintenance of polar growth and morphological patterning. Three families of cellular transport proteins, PIN-formed (PIN), P-glycoprotein (ABCB/PGP), and AUXIN RESISTANT 1/LIKE AUX1 (AUX1/LAX), can independently and co-ordinately transport auxin in plants. Regulation of these proteins involves intricate and co-ordinated cellular processes, including protein-protein interactions, vesicular trafficking, protein phosphorylation, ubiquitination, and stabilization of the transporter complexes on the plasma membrane.

ABCB19/PGP19 stabilises PIN1 in membrane microdomains in Arabidopsis.

Auxin transport is mediated at the cellular level by three independent mechanisms that are characterised by the PIN-formed (PIN), P-glycoprotein (ABCB/PGP) and AUX/LAX transport proteins. The PIN and ABCB transport proteins, best represented by PIN1 and ABCB19 (PGP19), have been shown to coordinately regulate auxin efflux. When PIN1 and ABCB19 coincide on the plasma membrane, their interaction enhances the rate and specificity of auxin efflux and the dynamic cycling of PIN1 is reduced.

Arabidopsis P-glycoprotein19 participates in the inhibition of gravitropism by gravacin.

ATP-binding cassette (ABC) transporters have been implicated in a multitude of biological pathways. In plants, some ABC transporters are involved in the polar transport of the plant hormone auxin and the gravitropic response. We previously identified Gravacin as a potent inhibitor of gravitropism in Arabidopsis thaliana.

Differential effects of sucrose and auxin on localized phosphate deficiency-induced modulation of different traits of root system architecture in Arabidopsis.

Phosphorus, one of the essential elements for plants, is often a limiting nutrient in soils. Low phosphate (Pi) availability induces sugar-dependent systemic expression of genes and modulates the root system architecture (RSA). Here, we present the differential effects of sucrose (Suc) and auxin on the Pi deficiency responses of the primary and lateral roots of Arabidopsis (Arabidopsis thaliana).

Interactions among PIN-FORMED and P-glycoprotein auxin transporters in Arabidopsis.

Directional transport of the phytohormone auxin is established primarily at the point of cellular efflux and is required for the establishment and maintenance of plant polarity. Studies in whole plants and heterologous systems indicate that PIN-FORMED (PIN) and P-glycoprotein (PGP) transport proteins mediate the cellular efflux of natural and synthetic auxins. However, aromatic anion transport resulting from PGP and PIN expression in nonplant systems was also found to lack the high level of substrate specificity seen in planta.

PGP4, an ATP binding cassette P-glycoprotein, catalyzes auxin transport in Arabidopsis thaliana roots.

Members of the ABC (for ATP binding cassette) superfamily of integral membrane transporters function in cellular detoxification, cell-to-cell signaling, and channel regulation. More recently, members of the multidrug resistance P-glycoprotein (MDR/PGP) subfamily of ABC transporters have been shown to function in the transport of the phytohormone auxin in both monocots and dicots. Here, we report that the Arabidopsis thaliana MDR/PGP PGP4 functions in the basipetal redirection of auxin from the root tip.

Cellular efflux of auxin catalyzed by the Arabidopsis MDR/PGP transporter AtPGP1.

Directional transport of the phytohormone auxin is required for the establishment and maintenance of plant polarity, but the underlying molecular mechanisms have not been fully elucidated. Plant homologs of human multiple drug resistance/P-glycoproteins (MDR/PGPs) have been implicated in auxin transport, as defects in MDR1 (AtPGP19) and AtPGP1 result in reductions of growth and auxin transport in Arabidopsis (atpgp1, atpgp19), maize (brachytic2) and sorghum (dwarf3). Here we examine the localization, activity, substrate specificity and inhibitor sensitivity of AtPGP1.