The transport of auxin controls the rate, direction and localization of plant growth and development. The course of auxin transport is defined by the polar subcellular localization of the PIN proteins, a family of auxin efflux transporters. However, little is known about the composition and regulation of the PIN protein complex. Here, using blue‐native PAGE and quantitative mass spectrometry, we identify native PIN core transport units as homo‐ and heteromers assembled from PIN1, PIN2, PIN3, PIN4 and PIN7 subunits only. Furthermore, we show that endogenous flavonols stabilize PIN dimers to regulate auxin efflux in the same way as does the auxin transport inhibitor 1‐naphthylphthalamic acid (NPA). This inhibitory mechanism is counteracted both by the natural auxin indole‐3‐acetic acid and by phosphomimetic amino acids introduced into the PIN1 cytoplasmic domain. Our results lend mechanistic insights into an endogenous control mechanism which regulates PIN function and opens the way for a deeper understanding of the protein environment and regulation of the polar auxin transport complex.

中文翻译：

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黄酮醇介导的 PIN 流出复合物稳定调节极性生长素转运


生长素的运输控制着植物生长和发育的速率、方向和定位。生长素转运的过程由 PIN 蛋白（生长素外流转运蛋白家族）的极性亚细胞定位决定。然而，人们对 PIN 蛋白复合物的组成和调控知之甚少。在这里，使用蓝色天然 PAGE 和定量质谱法，我们将天然 PIN 核心转运单元鉴定为仅由 PIN1、PIN2、PIN3、PIN4 和 PIN7 亚基组装而成的同聚体和异聚体。此外，我们发现内源性黄酮醇可以稳定 PIN 二聚体，以与生长素转运抑制剂 1-萘基邻苯二甲酸 (NPA) 相同的方式调节生长素流出。这种抑制机制被天然生长素吲哚-3-乙酸和引入 PIN1 胞质结构域的拟磷氨基酸所抵消。我们的结果为调节 PIN 功能的内源性控制机制提供了机制上的见解，并为更深入地了解蛋白质环境和极性生长素运输复合物的调节开辟了道路。