AGC kinases and MAB4/MEL proteins maintain PIN polarity by limiting lateral diffusion in plant cells

Shutang Tan,Remko Offringa,Ludmila Včelařová,Maritza Van Dop,Eike H Rademacher ,Matouš Glanc,Xiaoyu Wei,Bert De Rybel,Satoshi Naramoto,Lukas Hoermayer,Xixi Zhang,Robert Hauschild,Alexander Johnson,Gergely Molnár,Stef Janson,Edward De Koning,Jiřı́ Friml ,David Domjan,Matyáš Fendrych,Kasper Van Gelderen

doi:10.1016/j.cub.2021.02.028

Abstract

SummaryPolar subcellular localization of the PIN exporters 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. Arabidopsis mutants lacking PID, a kinase that phosphorylates PINs, or the MAB4/MEL proteins of unknown molecular function display PIN polarity defects and phenocopy pin mutants, but mechanistic insights into how these factors convey PIN polarity are missing. 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. 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. 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. We thus uncover the molecular mechanism by which AGC kinases and MAB4/MEL proteins regulate PIN localization and plant development.

Highlights

Auxin is a versatile regulator of plant growth and development
PINs recruit MAB4/MELs to different polar domains at the plasma membrane (PM) To understand the molecular mechanisms governing PIN polarity, we first investigated the inter-dependency of the remarkable colocalization of the PIN and MAB4/MEL proteins.[26]
MAB4/MELs and PID limit PIN lateral diffusion Having established the existence of the PIN-MAB4/MEL-AGC kinase protein complex, we addressed the actual molecular mechanism underlying its role in mediating PIN polarity

Summary

Introduction

Plants perceive and integrate various internal and external stimuli into local auxin maxima and minima, which are translated into different developmental outputs. This asymmetric distribution of auxin is achieved mainly through polar auxin transport, which is in turn heavily dependent on the polar subcellular plasma membrane (PM) localization of the PIN-FORMED (PIN) auxin efflux carriers.[1,2,3,4,5]. Studies of the canonical Cdc[42] polarity establishment pathway have established protein phosphorylation, specific lateral diffusion rates of different polarity proteins, and positive feedback as key mechanisms of symmetry breaking.[13,14] in the case of PIN polarity establishment and/ or maintenance, a role of limited lateral diffusion has been suggested;[15,16] its mechanistic basis is not understood

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