The phytohormone auxin is polarly transported in plants by PIN-FORMED (PIN) transporters and controls virtually all growth and developmental processes. Canonical PINs possess a long, largely disordered cytosolic loop. Auxin transport by canonical PINs is activated by loop phosphorylation by certain kinases. The structure of the PIN transmembrane domains was recently determined, their transport properties remained poorly characterized, and the role of the loop in the transport process was unclear. Here, we determined the quantitative kinetic parameters of auxin transport mediated by Arabidopsis PINs to mathematically model auxin distribution in roots and to test these predictions in vivo. Using chimeras between transmembrane and loop domains of different PINs, we demonstrate a strong correlation between transport parameters and physiological output, indicating that the loop domain is not only required to activate PIN-mediated auxin transport, but it has an additional role in the transport process by a currently unknown mechanism.

中文翻译：

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拟南芥经典 PIN-FORMED 蛋白的转运特性和环结构域在生长素转运中的作用


植物激素生长素在 PIN 形成 （PIN） 转运蛋白中通过植物极性运输，几乎控制所有生长和发育过程。经典 PIN 具有一个长的、基本上无序的胞质环。经典 PIN 的生长素转运被某些激酶的环磷酸化激活。最近确定了 PIN 跨膜结构域的结构，它们的运输特性仍然很差，并且环在运输过程中的作用尚不清楚。在这里，我们确定了拟南芥 PIN 介导的生长素转运的定量动力学参数，以数学方式模拟根中生长素的分布，并在体内测试这些预测 。使用不同 PIN 的跨膜和环结构域之间的嵌合体，我们证明了运输参数和生理输出之间的强相关性，表明环结构域不仅是激活 PIN 介导的生长素运输所必需的，而且它通过目前未知的机制在运输过程中具有额外的作用。