Section of Molecular Genetics, Department of Biology, Utrecht University, Padualaan 8, Utrecht, The Netherlands.
Development. 2010 Oct;137(19):3245-55. doi: 10.1242/dev.052456.
Polar membrane cargo delivery is crucial for establishing cell polarity and for directional transport processes. In plants, polar trafficking mediates the dynamic asymmetric distribution of PIN FORMED (PIN) carriers, which drive polar cell-to-cell transport of the hormone auxin, thereby generating auxin maxima and minima that control development. The Arabidopsis PINOID (PID) protein kinase instructs apical PIN localization by phosphorylating PINs. Here, we identified the PID homologs WAG1 and WAG2 as new PIN polarity regulators. We show that the AGC3 kinases PID, WAG1 and WAG2, and not other plant AGC kinases, instruct recruitment of PINs into the apical recycling pathway by phosphorylating the middle serine in three conserved TPRXS(N/S) motifs within the PIN central hydrophilic loop. Our results put forward a model by which apolarly localized PID, WAG1 and WAG2 phosphorylate PINs at the plasma membrane after default non-polar PIN secretion, and trigger endocytosis-dependent apical PIN recycling. This phosphorylation-triggered apical PIN recycling competes with ARF-GEF GNOM-dependent basal recycling to promote apical PIN localization. In planta, expression domains of PID, WAG1 and WAG2 correlate with apical localization of PINs in those cell types, indicating the importance of these kinases for apical PIN localization. Our data show that by directing polar PIN localization and PIN-mediated polar auxin transport, the three AGC3 kinases redundantly regulate cotyledon development, root meristem size and gravitropic response, indicating their involvement in both programmed and adaptive plant development.
极性膜货物传递对于建立细胞极性和定向运输过程至关重要。在植物中，极性运输介导 PIN 形成（PIN）载体的动态不对称分布，这些载体驱动激素生长素的极性细胞间运输，从而产生控制发育的生长素最大值和最小值。拟南芥 PINOID（PID）蛋白激酶通过磷酸化 PIN 来指导顶端 PIN 的定位。在这里，我们鉴定了 PID 同源物 WAG1 和 WAG2 作为新的 PIN 极性调节剂。我们表明，AGC3 激酶 PID、WAG1 和 WAG2，而不是其他植物 AGC 激酶，通过磷酸化 PIN 中心亲水环内三个保守的 TPRXS（N/S）基序中的中间丝氨酸来指导 PIN 招募到顶端再循环途径。我们的结果提出了一个模型，即非极性定位的 PID、WAG1 和 WAG2 在默认非极性 PIN 分泌后在质膜上磷酸化 PIN，触发依赖内吞作用的顶端 PIN 再循环。这种磷酸化触发的顶端 PIN 再循环与 ARF-GEF GNOM 依赖性基底再循环竞争，以促进顶端 PIN 定位。在植物中，PID、WAG1 和 WAG2 的表达域与这些细胞类型中顶端定位的 PIN 相关，表明这些激酶对于顶端 PIN 定位的重要性。我们的数据表明，通过指导极性 PIN 定位和 PIN 介导的极性生长素运输，三种 AGC3 激酶冗余调节子叶发育、根分生组织大小和向重力性反应，表明它们参与了程序性和适应性植物发育。
