| Topic | Key takeaways | Key evidence | Key recent sources | URL |
|---|---|---|---|---|
| Definition | Arabidopsis thaliana PIN1 (UniProt Q9C6B8; At1g73590) is the canonical long PIN-FORMED auxin exporter matching the UniProt description for an auxin efflux carrier, not the unrelated animal PIN1 prolyl isomerase. It is a plasma-membrane transporter central to polar auxin transport. (pqac-00000001, pqac-00000003, pqac-00000007) | Nature structural work explicitly identifies Arabidopsis PIN1 with UniProt Q9C6B8 and shows PIN1-mediated auxin efflux in heterologous assays; reviews describe PIN1/2 as auxin exporters with 10 transmembrane helices and a long hydrophilic loop. Assays included cryo-EM and [3H]IAA efflux in HEK293F cells. (pqac-00000001, pqac-00000003) | Luschnig & Friml, 2024 Nov; Yang et al., 2022 Aug | https://doi.org/10.1038/s41467-024-54240-y ; https://doi.org/10.1038/s41586-022-05143-9 |
| Primary function | PIN1’s primary molecular function is auxin export, specifically transport of indole-3-acetic acid (IAA/IAA−) from the cytosol toward the apoplast to establish directional cell-to-cell auxin flow. Long PINs such as PIN1 are the major plasma-membrane auxin efflux carriers. (pqac-00000001, pqac-00000003, pqac-00000006) | PIN1 is described as the “main PIN auxin exporter” in Arabidopsis; in transport assays, loss or mutation of key residues increases cellular [3H]IAA retention and reduces net efflux. Chemiosmotic context: apoplast ~pH 5.5, cytosol ~pH 7.0, with IAAH diffusion inward and PIN-dependent IAA− export outward. (pqac-00000000, pqac-00000025, pqac-00000027) | Luschnig & Friml, 2024 Nov; Yang et al., 2022 Aug | https://doi.org/10.1038/s41467-024-54240-y ; https://doi.org/10.1038/s41586-022-05143-9 |
| Transport mechanism | Structural studies support an elevator-like alternating-access mechanism for PIN-family auxin transporters, with PIN1 captured in inward-facing apo, IAA-bound, and NPA-bound states. NPA competitively occupies the same intracellular pocket as auxin and locks the transporter in an inward-open state. (pqac-00000025, pqac-00000027, pqac-00000031) | PIN1 cryo-EM structures were solved at ~3.1–3.2 Å for apo/IAA/NPA states; IAA binds an intracellular pocket coordinated by residues including V51, N112, N478, I582. For the related PIN8 family structure, transporter domains rotate ~20° and move the binding site ~5 Å, supporting the elevator model. (pqac-00000025, pqac-00000029, pqac-00000028, pqac-00000030) | Luschnig & Friml, 2024 Nov; Yang et al., 2022 Aug; Ung et al., 2022 Jun | https://doi.org/10.1038/s41467-024-54240-y ; https://doi.org/10.1038/s41586-022-05143-9 ; https://doi.org/10.1038/s41586-022-04883-y |
| Substrate specificity and inhibitor pharmacology | PIN1 directly recognizes natural auxin IAA, while N-1-naphthylphthalamic acid (NPA) is a high-affinity competitive inhibitor of the same site. Current structural evidence supports IAA as the principal demonstrated substrate. (pqac-00000024, pqac-00000025, pqac-00000032) | ITC at pH 7.0: PIN1 binds IAA with Kd = 83 ± 10 µM and NPA with Kd = 0.15 ± 0.08 µM, showing several-hundred-fold tighter binding of NPA. V51A raised IAA Kd to 1.39 mM (~17-fold weaker than WT); N112A and I582A prevented IAA binding, and Y145A impaired both IAA transport and NPA inhibition. (pqac-00000024, pqac-00000025, pqac-00000032) | Yang et al., 2022 Aug | https://doi.org/10.1038/s41586-022-05143-9 |
| Energetics | PIN-family transport appears largely independent of classical proton or ion gradients in available biochemical systems, although the in vivo energy source for PIN1 remains unresolved. Expert synthesis therefore favors a uniport-like mechanism but does not fully exclude context-dependent coupling in planta. (pqac-00000025, pqac-00000030, pqac-00000031) | For PIN1, no significant difference in relative [3H]IAA retention was observed between pH 5.5 and 6.5 in the cited assay. For PIN8, activity was reported as minimally pH-dependent, insensitive to proton-motive-force decouplers, and retained in sodium- or potassium-exclusive buffers; authors concluded the data support a uniport mechanism. (pqac-00000025, pqac-00000030, pqac-00000031) | Luschnig & Friml, 2024 Nov; Yang et al., 2022 Aug; Ung et al., 2022 Jun | https://doi.org/10.1038/s41467-024-54240-y ; https://doi.org/10.1038/s41586-022-05143-9 ; https://doi.org/10.1038/s41586-022-04883-y |
| Localization | PIN1 is a canonical long PIN predominantly localized asymmetrically at the plasma membrane, especially with basal polarity in vascular tissues and dynamic localization in shoot meristems and developing organs. Its polar localization determines auxin flow direction. (pqac-00000001, pqac-00000003, pqac-00000015) | Reviews highlight basal PIN1 localization in stem vasculature matching known auxin transport routes; PIN1 is widely expressed in embryos, meristems, and vascular tissues. Long PINs localize to the PM and are dynamically regulated by endocytosis and recycling. (pqac-00000001, pqac-00000003) | Luschnig & Friml, 2024 Nov; Yang et al., 2022 Aug | https://doi.org/10.1038/s41467-024-54240-y ; https://doi.org/10.1038/s41586-022-05143-9 |
| Regulation: phosphorylation and trafficking | PIN1 polarity, abundance, and activity are tightly regulated by phosphorylation and membrane trafficking. PID/WAG kinases bias apical sorting/polarity, D6PK stimulates transport activity, GNOM-dependent trafficking maintains polar domains, and ubiquitin/vacuolar pathways tune turnover. (pqac-00000018, pqac-00000021, pqac-00000023, pqac-00000026) | PID/WAG target conserved hydrophilic-loop phosphosites and can shift PIN1 from basal to apical localization; pid mutants phenocopy pin1-like naked inflorescences. D6PK activates PIN1 in HEK293F [3H]IAA efflux assays. Brefeldin A-sensitive GNOM controls recycling; reversible K63-linked polyubiquitination promotes vacuolar targeting. (pqac-00000021, pqac-00000018, pqac-00000026) | Luschnig & Friml, 2024 Nov; Wang et al., 2023 Jan; Yang et al., 2022 Aug | https://doi.org/10.1038/s41467-024-54240-y ; https://doi.org/10.1038/s41467-023-36200-0 ; https://doi.org/10.1038/s41586-022-05143-9 |
| Recent regulation advances (2023-2024) | Recent work links PIN1 control to phosphoinositide signaling, CLE peptide signaling, and ENHANCER OF PINOID (ENP), refining the view that PIN1 behavior is embedded in multiprotein polarity modules rather than controlled by phosphorylation alone. (pqac-00000016, pqac-00000017, pqac-00000019, pqac-00000020) | In developing protophloem, CLE45-BAM3-PBL signaling antagonizes PIP5K-dependent phosphoinositide control of PAX/BRX rheostat polarity, thereby affecting PIN1 patterning; imaging quantification used n = 19–51 roots and 210–540 PPSEs per genotype, with p < 0.0001 in reported comparisons. ENP bioRxiv 2024 showed its IDR interacts with PINs and is required to recruit/support PIN1 at apical PM domains; enp pid double mutants lacked cotyledons and flowers. (pqac-00000016, pqac-00000019, pqac-00000020) | Wang et al., 2023 Jan 27; Matthes et al., 2024 Mar 11; Luschnig & Friml, 2024 Nov | https://doi.org/10.1038/s41467-023-36200-0 ; https://doi.org/10.1101/2024.03.11.584374 ; https://doi.org/10.1038/s41467-024-54240-y |
| Developmental roles | PIN1 is a master regulator of auxin-dependent patterning in embryogenesis, organ initiation, phyllotaxis, vascular formation/canalization, and reproductive development. Its developmental effects are best explained by its role in creating local auxin maxima and directional fluxes. (pqac-00000009, pqac-00000012, pqac-00000014) | pin1 loss-of-function mutants produce naked, pin-like inflorescences or sterile stems lacking normal flowers; pid mutants show a similar phenotype. Reviews and modeling connect PIN1 to organ initiation, lateral organ positioning, embryonic axis formation, vascular patterning, and female gametophyte development. (pqac-00000009, pqac-00000012, pqac-00000013, pqac-00000015) | Kong et al., 2024 Jul; Luschnig & Friml, 2024 Nov | https://doi.org/10.1038/s41467-024-50172-9 ; https://doi.org/10.1038/s41467-024-54240-y |
| Reproductive and ovule-associated roles | PIN1-mediated auxin transport contributes to gynoecium, carpel, and ovule patterning, linking sporophytic auxin transport to seed-setting capacity. In these contexts, localization and transport inhibition studies support a spatial patterning role rather than a direct enzymatic one. (pqac-00000011) | PIN1 localizes in ovule primordia, developing nucellus, and funiculus. NPA treatment altered carpel auxin gradients and caused increased stigma/style elongation, basalized style/ovary boundary, reduced ovary production, fewer carpel valves, and altered ovule initiation along the placenta. (pqac-00000011) | Reiter, 2025; synthesized against 2024 review context | N/A |
| Applications and real-world implementation | Direct translational deployment of AtPIN1 itself was not demonstrated in the gathered Arabidopsis-specific sources, but the evidence supports PIN1 as a validated mechanistic target for engineering plant architecture through auxin transport control. Real-world implementation in this evidence base is strongest at the level of chemical inhibition (NPA) and developmental modeling/reporter systems. (pqac-00000000, pqac-00000014, pqac-00000016) | Practical implementations in the gathered studies include use of NPA to manipulate auxin transport and morphology, pPIN1::PIN1-GFP reporter lines to monitor polarity, and quantitative image-based protophloem analyses with large sample sizes. Structural resolution of the IAA/NPA pocket provides a framework for future rational modulation of auxin transport. (pqac-00000011, pqac-00000014, pqac-00000016, pqac-00000032) | Wang et al., 2023 Jan 27; Kong et al., 2024 Jul 18; Luschnig & Friml, 2024 Nov; Yang et al., 2022 Aug | https://doi.org/10.1038/s41467-023-36200-0 ; https://doi.org/10.1038/s41467-024-50172-9 ; https://doi.org/10.1038/s41467-024-54240-y ; https://doi.org/10.1038/s41586-022-05143-9 |


*Table: This table summarizes the verified identity, function, mechanism, regulation, localization, developmental roles, and application-relevant findings for Arabidopsis thaliana PIN1 (Q9C6B8). It prioritizes 2023-2024 sources where available and includes quantitative evidence such as binding affinities, assay types, and sample sizes.*