Orchestration of microtubules and the actin cytoskeleton in trichome cell shape determination by a plant-unique kinesin.

Juan Tian,Weiwei Liu,Yinping Ma,Guangda Wang,Zhaosheng Kong,Libo Han,Zhidi Feng,Yanjun Yu

doi:10.7554/elife.09351

Abstract

Microtubules (MTs) and actin filaments (F-actin) function cooperatively to regulate plant cell morphogenesis. However, the mechanisms underlying the crosstalk between these two cytoskeletal systems, particularly in cell shape control, remain largely unknown. In this study, we show that introduction of the MyTH4-FERM tandem into KCBP (kinesin-like calmodulin-binding protein) during evolution conferred novel functions. The MyTH4 domain and the FERM domain in the N-terminal tail of KCBP physically bind to MTs and F-actin, respectively. During trichome morphogenesis, KCBP distributes in a specific cortical gradient and concentrates at the branching sites and the apexes of elongating branches, which lack MTs but have cortical F-actin. Further, live-cell imaging and genetic analyses revealed that KCBP acts as a hub integrating MTs and actin filaments to assemble the required cytoskeletal configuration for the unique, polarized diffuse growth pattern during trichome cell morphogenesis. Our findings provide significant insights into the mechanisms underlying cytoskeletal regulation of cell shape determination.

Highlights

Plant cells assume an amazing diversity of cell shapes that enable these cells to execute unique physiological functions, and the study of plant cell shape determination has remained an intriguing part of plant biology (Smith and Oppenheimer, 2005; Szymanski, 2009)
Whether kinesin-like calmodulin-binding protein (KCBP) localizes to cortical MTs in trichome cells is still an open question, cellular basis of defects in kcbp trichomes needs to be examined, direct evidence linking KCBP and F-actin is currently missing, and the role of the mysterious MyTH4-FERM domain remains to be unraveled
To determine whether KCBP localizes to cortical MTs, we performed live-cell imaging using a functional, GFP-tagged KCBP fusion under the control of its endogenous regulatory elements; this construct fully rescued the typical zwichel trichome defects in the kcbp-1 (Salk_031704 in the Arabidopsis Biological Resource Center; see ‘Materials and methods’) mutant (Figure 1—figure supplement 1A) (Humphrey et al, 2015), which was designated as zwiA (N531704 in the Nottingham Arabidopsis Stock Centre; see ‘Materials and methods’) (Buschmann et al, 2015)

Summary

Introduction

Plant cells assume an amazing diversity of cell shapes that enable these cells to execute unique physiological functions, and the study of plant cell shape determination has remained an intriguing part of plant biology (Smith and Oppenheimer, 2005; Szymanski, 2009). The plant cytoskeletal system, composed of microtubules (MTs) and actin filaments (F-actin), plays a central role in cell morphogenesis in both tip-growing and diffuse-growing cell types. F-actin plays central roles in polarized cell elongation, mainly by regulating intracellular transport (Hussey et al, 2006). Despite emerging evidence that cortical MTs and F-actin coordinately regulate plant cell morphogenesis (Petrasek and Schwarzerova, 2009; Sampathkumar et al, 2011; Sambade et al, 2014), the molecular mechanisms underlying the crosstalk between these two cytoskeletal systems remain largely unknown. Actin filaments mainly affect elongation of trichomes, and disruption of genes encoding actin-related proteins, such as components of the ARP2/3 actin nucleation complex and the upstream

Methods

Results

Conclusion