Institute of Biology II, University of Freiburg, Freiburg, Germany.
Institute of Physiology II, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
EMBO J. 2021 Jan 4;40(1):e104416. doi: 10.15252/embj.2020104416. Epub 2020 Nov 13.
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.
生长素的运输控制着植物生长和发育的速度、方向和定位。生长素运输的过程由 PIN 蛋白的极性亚细胞定位定义，PIN 蛋白是一类生长素外排转运蛋白。然而，PIN 蛋白复合物的组成和调节仍知之甚少。在这里，我们使用蓝色非变性 PAGE 和定量质谱法，鉴定出天然的 PIN 核心转运单元是由 PIN1、PIN2、PIN3、PIN4 和 PIN7 亚基组成的同源和异源二聚体。此外，我们还表明，内源性类黄酮稳定 PIN 二聚体以调节生长素外排，其方式与生长素运输抑制剂 1-萘基邻氨甲酰苯甲酸（NPA）相同。这种抑制机制被天然生长素吲哚-3-乙酸和引入 PIN1 细胞质结构域的磷酸模拟氨基酸所抵消。我们的研究结果为调节 PIN 功能的内源性控制机制提供了机制上的见解，并为深入了解极性生长素运输复合物的蛋白质环境和调节开辟了道路。
