背景回顾：Polar subcellular localization of the PINexporters of the phytohormone auxin is a key determinant of directional, intercellular auxin transport and thus a central topic of both plant cell and developmental biology.

提出问题：Arabidopsis mutants lacking PID, a kinase that phosphorylates PINs, or the MAB4/MELproteins of unknown molecular function display PIN polarity defects and phenocopy pin mutants, but mechanistic insights into how these factors convey PIN polarity are missing. 

结果1-互作复合体：Here, by combining protein biochemistry with quantitative live-cell imaging, we demonstrate that PINs, MAB4/MELs, and AGC kinases interact in the same complex at the plasma membrane. 

结果2-PIN招募MAB4/MELs：MAB4/MELs are recruited to the plasma membrane by the PINs and in concert with the AGC kinases maintain PIN polarity through limiting lateral diffusion-based escape of PINs from the polar domain. 

结果3-正反馈调节：The PIN-MAB4/MEL-PID protein complex has self-reinforcing properties thanks to positive feedback between AGC kinase-mediated PIN phosphorylation and MAB4/MEL recruitment. 

结论：We thus uncover the molecular mechanism by which AGC kinases and MAB4/MEL proteins regulate PIN localization and plant development.

 摘 要 

生长素外运载体PIN蛋白在细胞中的极性定位是决定细胞间方向性生长素流的关键因素，因此在植物细胞和发育生物学领域备受关注。拟南芥中，PID能够磷酸化PINs，而MAB4/MEL蛋白还未知其生物学功能，但是二者的突变体均表现出PIN蛋白的极性定位缺陷，出现类似于pin突变体的表型，但是这两种蛋白具体如何作用于PINs的极性还不清楚。本文中，作者结合了蛋白生物化学和定量活细胞成像，发现PINs、MAB4/MELs和AGC激酶在质膜上的同一个复合体中发生互作。MAB4/MELs被PINs招募到质膜，并在此与AGC激酶一起通过限制PIN在极性域中的侧向扩散，来维持PIN的极性。PIN-MAB4/MEL-PID蛋白复合体具有自我增强的特性，这是由AGC激酶介导的PIN磷酸化和MAB4/MEL招募形成的正向反馈所介导的。因此，本文的研究揭示了一个AGC激酶和MAB4/MEL蛋白作用于PIN蛋白的极性定位， 从而调控植物发育的分子机制。

 通讯作者 

** Jiří Friml **