The Circular F-Actin Bundles Provide a Track for Turnaround and Bidirectional Movement of Mitochondria in Arabidopsis Root Hair

Yu Zhang,Yan Li,Xiaojing Sheng,Xiangfei Meng,James M Ervasti

doi:10.1371/journal.pone.0091501

Abstract

BackgroundThe movement of organelles in root hairs primarily occurs along the actin cytoskeleton. Circulation and “reverse fountain” cytoplasmic streaming constitute the typical forms by which most organelles (such as mitochondria and the Golgi apparatus) in plant root hair cells engage in bidirectional movement. However, there remains a lack of in-depth research regarding the relationship between the distribution of the actin cytoskeleton and turnaround organelle movement in plant root hair cells.ResultsIn this paper, Arabidopsis seedlings that had been stably transformed with a GFP-ABD2-GFP (green fluorescent protein-actin-binding domain 2-green fluorescent protein) construct were utilized to study the distribution of bundles of filamentous (F)-actin and the directed motion of mitochondria along these bundles in root hairs. Observations with a confocal laser scanning microscope revealed that there were widespread circular F-actin bundles in the epidermal cells and root hairs of Arabidopsis roots. In root hairs, these circular bundles primarily start at the sub-apical region, which is the location where the turnaround movement of organelles occurs. MitoTracker probes were used to label mitochondria, and the dynamic observation of root hair cells with a confocal laser scanning microscope indicated that turnaround mitochondrial movement occurred along circular F-actin bundles.ConclusionsRelevant experimental results demonstrated that the circular F-actin bundles provide a track for the turnaround and bidirectional movement of mitochondria.

Highlights

The actin cytoskeleton is an important component for the establishment of polarity in plant cells [1]; in combination with myosin, the actin cytoskeleton promotes organelle movement within cells [2,3]
Observations of root hairs prepared through freezing and chemical fixation indicated the absence of F-actin bundles in a small region at the apex of these hairs [6,8], and approaches that have used fluorescein isothiocyanate (FITC)-phalloidin microinjections or green fluorescent protein (GFP)-fused actin-binding proteins to label F-actin revealed only a modicum of disorganized filaments at the apex of Arabidopsis root hairs [9,10]
We found that the GFP-actinbinding domain 2 (ABD2)-GFP stable expression root hairs were similar to wild type root hairs in length and morphology (Figure S1)

Summary

Introduction

The actin cytoskeleton is an important component for the establishment of polarity in plant cells [1]; in combination with myosin, the actin cytoskeleton promotes organelle movement within cells [2,3]. Root hairs are an important model system for the study of organelle movement and the cytoskeleton in plant cells. Observations of root hairs prepared through freezing and chemical fixation indicated the absence of F-actin bundles in a small region at the apex of these hairs [6,8], and approaches that have used fluorescein isothiocyanate (FITC)-phalloidin microinjections or green fluorescent protein (GFP)-fused actin-binding proteins to label F-actin revealed only a modicum of disorganized filaments at the apex of Arabidopsis root hairs [9,10]. There remains a lack of in-depth research regarding the relationship between the distribution of the actin cytoskeleton and turnaround organelle movement in plant root hair cells

Methods

Results

Conclusion