Synthetic auxin herbicides like 2,4-dichlorophenoxyacetic acid (2,4-D) are widely used in agriculture to control dicot weeds, yet the identity of their transporters in plant cells has remained unresolved. While natural auxins \u2013 such as indole-3-acetic acid (IAA), key phytohormones that regulate plant growth and development \u2013 are known to be transported by PIN-FORMED (PIN) auxin exporters, it has been unclear whether structurally similar herbicides also rely on these transporters or diffuse passively.<\/p>\n
A recent study led by Ulrich Hammes and Bj\u00f8rn Pedersen addresses this long-standing question by demonstrating that several phenoxyacetic acid herbicides are actively transported by PIN proteins, particularly PIN8. Using solid-supported membrane electrophysiology (SSME, SURFE\u00b2R), the researchers recorded electrogenic transport of 2,4-D and 4-chlorophenoxyacetic acid (4-CPA). Transport was inhibited by the auxin efflux blocker NPA, confirming transporter-mediated export with measurable affinities comparable to that of IAA.<\/p>\n
The study also employed cryo-electron microscopy (cryo-EM) to capture five conformational states of PIN8 bound to 2,4-D or 4-CPA, revealing a stepwise transport cycle with distinct ligand poses representing prebinding, binding, and release. Mutagenesis of residues involved in coordinating herbicide carboxyl or halogen groups \u2013 such as Asn117, Tyr150, and Ser55 \u2013 validated these structural snapshots and pinpointed the molecular determinants of substrate specificity.<\/p>\n
Overall, this work reveals that phenoxyacetic acid herbicides utilize the same export machinery as endogenous auxins and resolves a major controversy in plant hormone transport biology. It also showcases SSME as a powerful tool for probing electrogenic transport in plant membrane proteins. By mapping herbicide transport at atomic resolution, the study lays the groundwork for structure-guided design of new auxin analogs and the engineering of herbicide-resistant crops.<\/p>\n
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\nFind the full article here: Transport of phenoxyacetic acid herbicides by PIN-FORMED auxin transporters<\/a><\/p>\n