Connective Auxin Transport in the Shoot Facilitates Communication between Shoot Apices.

Tom Bennett,Megan G Sawchuk,Tanya Waldie,Ottoline Leyser,Geneviève Hines,Enrico Scarpella,Karin Ljung,Martin Van Rongen,Jason Reed

doi:10.1371/journal.pbio.1002446

Abstract

The bulk polar movement of the plant signaling molecule auxin through the stem is a long-recognized but poorly understood phenomenon. Here we show that the highly polar, high conductance polar auxin transport stream (PATS) is only part of a multimodal auxin transport network in the stem. The dynamics of auxin movement through stems are inconsistent with a single polar transport regime and instead suggest widespread low conductance, less polar auxin transport in the stem, which we term connective auxin transport (CAT). The bidirectional movement of auxin between the PATS and the surrounding tissues, mediated by CAT, can explain the complex auxin transport kinetics we observe. We show that the auxin efflux carriers PIN3, PIN4, and PIN7 are major contributors to this auxin transport connectivity and that their activity is important for communication between shoot apices in the regulation of shoot branching. We propose that the PATS provides a long-range, consolidated stream of information throughout the plant, while CAT acts locally, allowing tissues to modulate and be modulated by information in the PATS.

Highlights

The polar auxin transport stream (PATS) can be defined as a long distance transport route carrying the plant hormone auxin from growing shoot tips towards the roots
Auxin is produced in growing shoot tips and transported down the main stem in the Polar Auxin Transport Stream (PATS)
We have previously shown that communication between shoot tips is mediated at least in part by competition between buds for access to the PATS

Summary

Introduction

The polar auxin transport stream (PATS) can be defined as a long distance transport route carrying the plant hormone auxin from growing shoot tips towards the roots. Molecular genetic studies in Arabidopsis thaliana identified such a family of auxin efflux carriers—the PIN-FORMED (PIN) proteins—which are often polarly localized [6,7,8,9]. This family includes the PIN1 protein, which has been shown to be polarly localized in the xylem parenchyma and vascular cambium of stems, which are major sites for the PATS [3,9,10].

Methods

Results

Discussion

Conclusion