ER-Localized PIN Carriers: Regulators of Intracellular Auxin Homeostasis.

Nayyer Abdollahi Sisi,Kamil Růžička

doi:10.3390/plants9111527

Abstract

The proper distribution of the hormone auxin is essential for plant development. It is channeled by auxin efflux carriers of the PIN family, typically asymmetrically located on the plasma membrane (PM). Several studies demonstrated that some PIN transporters are also located at the endoplasmic reticulum (ER). From the PM-PINs, they differ in a shorter internal hydrophilic loop, which carries the most important structural features required for their subcellular localization, but their biological role is otherwise relatively poorly known. We discuss how ER-PINs take part in maintaining intracellular auxin homeostasis, possibly by modulating the internal levels of IAA; it seems that the exact identity of the metabolites downstream of ER-PINs is not entirely clear as well. We further review the current knowledge about their predicted structure, evolution and localization. Finally, we also summarize their role in plant development.

Highlights

The systematic effort of plant molecular biology has integrated the phytohormone auxin in key developmental processes
Besides auxin signaling, which is located in the nucleus, and controlled IAA synthesis and degradation, which occurs in various cellular compartments, the critical role of the cell-to-cell auxin transport has been classically underlined [4]
The genome of Arabidopsis thaliana encodes eight PIN-FORMED family transporters (PINs) proteins. Based on their mutual sequence similarity and subcellular localization, they are categorized into two basic sub-clades (Figure 1): plasma membrane (PM- or long) and endoplasmic reticulum (ER- or short) PINs [12,16]

Summary

Introduction

The systematic effort of plant molecular biology has integrated the phytohormone auxin in key developmental processes. Besides auxin signaling, which is located in the nucleus, and controlled IAA synthesis and degradation, which occurs in various cellular compartments, the critical role of the cell-to-cell auxin transport has been classically underlined [4]. In line with this concept, auxin is directionally conveyed by the PIN-FORMED family transporters (PINs) that are typically asymmetrically localized at the plasma membrane (PM) [5]. The genome of Arabidopsis thaliana encodes eight PIN proteins Based on their mutual sequence similarity and subcellular localization, they are categorized into two basic sub-clades (Figure 1): plasma membrane (PM- or long) and endoplasmic reticulum (ER- or short) PINs [12,16]. PM: PINs present on PM, ER: PINs showing ER or dual PM and ER localization

Membrane Topology and Structural Properties of ER-PINs

Directionality of ER-PIN-Mediated Auxin Fluxes

Evolution of ER-PINs in Plants

Role of ER-PINs in in Intracellular

Role of ER-PINs in Plant Development

Conclusions