MAP kinase regulation of PIN-FORMED auxin transporters

生长素是一种可移动的植物激素，通过分布极广的PIN生长素外排转运蛋白的活性在细胞间定向运输。了解生长素的运输活性和定向运输对于理解植物发育的基本过程具有重要意义。近年来，我们和其他人阐明了保守的丝氨酸(S)残基上的PIN磷酸化对PIN活性、质膜分布和极性的调节作用。值得注意的是，在高度保守的T1PRXS1-T3PRXS3基序中，PIN激活和极性控制所需的三个PIN丝氨酸残基S1-S3位于假设的MAP激酶靶向苏氨酸磷酸酶T1-T3附近。T1-T3亚磷酸盐磷酸化以及共同调节的S337 MAP激酶靶点对PIN功能的作用尚不清楚。在这里，我建议使用亚磷酸盐特异性抗体的免疫染色和定量磷蛋白质组学来研究T亚磷酸盐磷酸化的分布和丰度，以及与S亚磷酸盐磷酸化共同作用的分布和丰度。此外，我建议研究MAP信号突变体中这些磷酸化的丰度，以在植物中确定T磷酸化所需的MAP信号级联。最后，我建议利用遗传学、细胞生物学和生理学相结合的方法，分离并结合S1-S3磷酸化来研究T亚磷酸盐磷酸化在PIN激活、极性控制和其他细胞生物学功能中的作用。

Auxin is a mobile plant hormone that is directionally transported from cell-to-cell through the activity of polarly distributed PIN auxin efflux transporters. Understanding auxin transport activity and directional transport is of great importance for the understanding of fundamental processes in plant development. In recent years, we and others have elucidated the role of PIN phosphorylation at conserved serine (S) residues for the regulation of PIN activity, plasma membrane distribution and polarity. Strikingly, three PIN serine residues required for PIN activation and polarity control, S1 – S3, reside in close proximity to hypothesized MAP kinase-targeted threonine phosphosites, T1 – T3, in the highly conserved T1PRXS1 – T3PRXS3 motifs. The role of T1 – T3 phosphosite phosphorylation, as well as that of a co-regulated S337 MAP kinase target site, for PIN function has not been elucidated as yet. Here, I propose to use immunostaining with phosphosite specific antibodies and quantitative phosphoproteomics to study the distribution and abundance of T phosphosite phosphorylation, alone and in conjunction with S phosphosite phosphorylation. Further, I propose to study the abundance of these phosphorylations in MAP signalling mutants to identify in planta MAP signalling cascades required for T phosphorylation. Finally, I propose to examine the role of T phosphosite phosphorylation for PIN activation, polarity control and other cell biological functions using a combination of genetics, cell biology and physiology, in isolation and together with S1 – S3 phosphorylation.