[1] [1] Adamowski, M., and Friml, J.(2015). PIN-dependent auxin transport: action, regulation, and evolution. Plant Cell27:20-32.

[2] [2] Afonine, P.V., Poon, B.K., Read, R.J., Sobolev, O.V., Terwilliger, T.C., Urzhumtsev, A., and Adams, P.D.(2018). Real-space refinement in PHENIX for cryo-EM and crystallography. Acta Crystallogr. D Struct. Biol.74:531-544.

[3] [3] Bennett, M.J., Marchant, A., Green, H.G., May, S.T., Ward, S.P., Millner, P.A., Walker, A.R., Schulz, B., and Feldmann, K.A.(1996). Arabidopsis AUX1 gene: a permease-like regulator of root gravitropism. Science273:948-950.

[4] [4] Carrier, D.J., Bakar, N.T.A., Swarup, R., Callaghan, R., Napier, R.M., Bennett, M.J., and Kerr, I.D.(2008). The binding of auxin to the Arabidopsis auxin influx transporter AUX1. Plant Physiol.148:529-535.

[5] [5] Del Alamo, D., Meiler, J., and McHaourab, H.S.(2022). Principles of Alternating Access in LeuT-fold Transporters: Commonalities and Divergences. J. Mol. Biol.434:167746.

[6] [6] Delbarre, A., Muller, P., Imhoff, V., and Guern, J.(1996). Comparison of mechanisms controlling uptake and accumulation of 2,4-dichlorophenoxy acetic acid, naphthalene-1-acetic acid, and indole-3-acetic acid in suspension-cultured tobacco cells. Planta198:532-541.

[7] [7] Emsley, P., and Cowtan, K.(2004). Coot: model-building tools for molecular graphics. Acta Crystallogr. D Biol. Crystallogr.60:2126-2132.

[8] [8] Geier, U., Werner, O., and Bopp, M.(1990). Indole-3-acetic acid uptake in isolated protoplasts of the moss Funaria hygrometrica. Physiol. Plantarum80:584-592.

[9] [9] Hertel, R., Lomax, T.L., and Briggs, W.R.(1983). Auxin transport in membrane vesicles from Cucurbita pepo L. Planta157:193-201.

[10] [10] Holm, L.(2022). Dali server: structural unification of protein families. Nucleic Acids Res.50:W210-W215.

[11] [11] Huang, L.K., Liao, Y.Y., Lin, W.H., Lin, S.M., Liu, T.Y., Lee, C.H., and Pan, R.L.(2019). Potassium Stimulation of IAA Transport Mediated by the Arabidopsis Importer AUX1 Investigated in a Heterologous Yeast System. J. Membr. Biol.252:183-194.

[12] [12] Jungnickel, K.E.J., Parker, J.L., and Newstead, S.(2018). Structural basis for amino acid transport by the CAT family of SLC7 transporters. Nat. Commun.9:550.

[13] [13] Kazmier, K., Claxton, D.P., and McHaourab, H.S.(2017). Alternating access mechanisms of LeuT-fold transporters: trailblazing towards the promised energy landscapes. Curr. Opin. Struct. Biol.45:100-108.

[14] [14] Korasick, D.A., Enders, T.A., and Strader, L.C.(2013). Auxin biosynthesis and storage forms. J. Exp. Bot.64:2541-2555.

[15] [15] Kramer, E.M., and Bennett, M.J.(2006). Auxin transport: a field in flux. Trends Plant Sci.11:382-386.

[16] [16] Krishnamurthy, H., and Gouaux, E.(2012). X-ray structures of LeuT in substrate-free outward-open and apo inward-open states. Nature481:469-474.

[17] [17] Lavy, M., and Estelle, M.(2016). Mechanisms of auxin signaling. Development143:3226-3229.

[18] [18] Lei, H.T., Ma, J., Sanchez Martinez, S., and Gonen, T.(2018). Crystal structure of arginine-bound lysosomal transporter SLC38A9 in the cytosol-open state. Nat. Struct. Mol. Biol.25:522-527.

[19] [19] Leyser, O.(2006). Dynamic integration of auxin transport and signalling. Curr. Biol.16:R424-R433.

[20] [20] Lomax, T.L., Mehlhorn, R.J., and Briggs, W.R.(1985). Active auxin uptake by zucchini membrane vesicles: quantitation using ESR volume and delta pH determinations. Proc. Natl. Acad. Sci. USA82:6541-6545.

[21] [21] Marchant, A., Kargul, J., May, S.T., Muller, P., Delbarre, A., Perrot-Rechenmann, C., and Bennett, M.J.(1999). AUX1 regulates root gravitropism in Arabidopsis by facilitating auxin uptake within root apical tissues. EMBO J.18:2066-2073.

[22] [22] Peret, B., Swarup, K., Ferguson, A., Seth, M., Yang, Y., Dhondt, S., James, N., Casimiro, I., Perry, P., Syed, A., et al.(2012). AUX/LAX genes encode a family of auxin influx transporters that perform distinct functions during Arabidopsis development. Plant Cell24:2874-2885.

[23] [23] Pettersen, E.F., Goddard, T.D., Huang, C.C., Couch, G.S., Greenblatt, D.M., Meng, E.C., and Ferrin, T.E.(2004). UCSF Chimera-a visualization system for exploratory research and analysis. J. Comput. Chem.25:1605-1612.

[24] [24] Pettersen, E.F., Goddard, T.D., Huang, C.C., Meng, E.C., Couch, G.S., Croll, T.I., Morris, J.H., and Ferrin, T.E.(2021). UCSF ChimeraX: Structure visualization for researchers, educators, and developers. Protein Sci.30:70-82.

[25] [25] Pickett, F.B., Wilson, A.K., and Estelle, M.(1990). The aux1 Mutation of Arabidopsis Confers Both Auxin and Ethylene Resistance. Plant Physiol.94:1462-1466.

[26] [26] Punjani, A., Rubinstein, J.L., Fleet, D.J., and Brubaker, M.A.(2017). cryoSPARC: algorithms for rapid unsupervised cryo-EM structure determination. Nat. Methods14:290-296.

[27] [27] Rahman, A., Ahamed, A., Amakawa, T., Goto, N., and Tsurumi, S.(2001). Chromosaponin I specifically interacts with AUX1 protein in regulating the gravitropic response of Arabidopsis roots. Plant Physiol.125:990-1000.

[28] [28] Rubery, P.H., and Sheldrake, A.R.(1973). Effect of pH and surface charge on cell uptake of auxin. Nat. New Biol.244:285-288.

[29] [29] Rubery, P.H., and Sheldrake, A.R.(1974). Carrier-mediated auxin transport. Planta118:101-121.

[30] [30] Schulz, L., Ung, K.L., Zuzic, L., Koutnik-Abele, S., Schiott, B., Stokes, D.L., Pedersen, B.P., and Hammes, U.Z.(2025). Transport of phenoxyacetic acid herbicides by PIN-FORMED auxin transporters. Nat. Plants.

[31] [31] Shaffer, P.L., Goehring, A., Shankaranarayanan, A., and Gouaux, E.(2009). Structure and mechanism of a Na+-independent amino acid transporter. Science325:1010-1014.

[32] [32] Singh, G., Retzer, K., Vosolsobe, S., and Napier, R.(2018). Advances in Understanding the Mechanism of Action of the Auxin Permease AUX1. Int. J. Mol. Sci.19:3391.

[33] [33] Song, Y.(2014). Insight into the mode of action of 2,4-dichlorophenoxyacetic acid (2,4-D) as an herbicide. J. Integr. Plant Biol.56:106-113.

[34] [34] Su, N., Zhu, A., Tao, X., Ding, Z.J., Chang, S., Ye, F., Zhang, Y., Zhao, C., Chen, Q., Wang, J., et al.(2022). Structures and mechanisms of the Arabidopsis auxin transporter PIN3. Nature609:616-621.

[35] [35] Swarup, R., and Bhosale, R.(2019). Developmental Roles of AUX1/LAX Auxin Influx Carriers in Plants. Front. Plant Sci.10:1306.

[36] [36] Swarup, R., Friml, J., Marchant, A., Ljung, K., Sandberg, G., Palme, K., and Bennett, M.(2001). Localization of the auxin permease AUX1 suggests two functionally distinct hormone transport pathways operate in the Arabidopsis root apex. Genes Dev.15:2648-2653.

[37] [37] Swarup, R., Kargul, J., Marchant, A., Zadik, D., Rahman, A., Mills, R., Yemm, A., May, S., Williams, L., Millner, P., et al.(2004). Structurefunction analysis of the presumptive Arabidopsis auxin permease AUX1. Plant Cell16:3069-3083.

[38] [38] Swarup, R., Kramer, E.M., Perry, P., Knox, K., Leyser, H.M.O., Haseloff, J., Beemster, G.T.S., Bhalerao, R., and Bennett, M.J.(2005). Root gravitropism requires lateral root cap and epidermal cells for transport and response to a mobile auxin signal. Nat. Cell Biol.7:1057-1065.

[39] [39] Swarup, R., and Pret, B.(2012). AUX/LAX family of auxin influx carriersan overview. Front. Plant Sci.3:225.

[40] [40] Teale, W.D., Paponov, I.A., and Palme, K.(2006). Auxin in action: signalling, transport and the control of plant growth and development. Nat. Rev. Mol. Cell Biol.7:847-859.

[41] [41] Ung, K.L., Winkler, M., Schulz, L., Kolb, M., Janacek, D.P., Dedic, E., Stokes, D.L., Hammes, U.Z., and Pedersen, B.P.(2022). Structures and mechanism of the plant PIN-FORMED auxin transporter. Nature609:605-610.

[42] [42] Vandenbussche, F., Petrsek, J., Zdnkov, P., Hoyerov, K., Pesek, B., Raz, V., Swarup, R., Bennett, M., Zazmalov, E., Benkov, E., and Van Der Straeten, D.(2010). The auxin influx carriers AUX1 and LAX3 are involved in auxin-ethylene interactions during apical hook development in Arabidopsis thaliana seedlings. Development137:597-606.

[43] [43] Vanneste, S., and Friml, J.(2009). Auxin: a trigger for change in plant development. Cell136:1005-1016.

[44] [44] Wang, R., and Estelle, M.(2014). Diversity and specificity: auxin perception and signaling through the TIR1/AFB pathway. Curr. Opin. Plant Biol.21:51-58.

[45] [45] Yamashita, A., Singh, S.K., Kawate, T., Jin, Y., and Gouaux, E.(2005). Crystal structure of a bacterial homologue of Na+/Cl-dependent neurotransmitter transporters. Nature437:215-223.

[46] [46] Yang, Y., Hammes, U.Z., Taylor, C.G., Schachtman, D.P., and Nielsen, E.(2006). High-affinity auxin transport by the AUX1 influx carrier protein. Curr. Biol.16:1123-1127.

[47] [47] Yang, Z., Wei, H., Gan, Y., Liu, H., Cao, Y., An, H., Que, X., Gao, Y., Zhu, L., Tan, S., et al.(2025). Structural insights into auxin influx mediated by the Arabidopsis AUX1. Cell.

[48] [48] Yang, Z., Xia, J., Hong, J., Zhang, C., Wei, H., Ying, W., Sun, C., Sun, L., Mao, Y., Gao, Y., et al.(2022). Structural insights into auxin recognition and efflux by Arabidopsis PIN1. Nature609:611-615.