The Cytoskeleton and Its Role in Determining Cellulose Microfibril Angle in Secondary Cell Walls of Woody Tree Species.

Tobias Tobias,Mcfarlane McFarlane,Bossinger Bossinger,Spokevicius Spokevicius

doi:10.3390/plants9010090

Tobias Tobias, Mcfarlane McFarlane + Show 2 more

Open Access

https://doi.org/10.3390/plants9010090

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Abstract

Recent advances in our understanding of the molecular control of secondary cell wall (SCW) formation have shed light on molecular mechanisms that underpin domestication traits related to wood formation. One such trait is the cellulose microfibril angle (MFA), an important wood quality determinant that varies along tree developmental phases and in response to gravitational stimulus. The cytoskeleton, mainly composed of microtubules and actin filaments, collectively contribute to plant growth and development by participating in several cellular processes, including cellulose deposition. Studies in Arabidopsis have significantly aided our understanding of the roles of microtubules in xylem cell development during which correct SCW deposition and patterning are essential to provide structural support and allow for water transport. In contrast, studies relating to SCW formation in xylary elements performed in woody trees remain elusive. In combination, the data reviewed here suggest that the cytoskeleton plays important roles in determining the exact sites of cellulose deposition, overall SCW patterning and more specifically, the alignment and orientation of cellulose microfibrils. By relating the reviewed evidence to the process of wood formation, we present a model of microtubule participation in determining MFA in woody trees forming reaction wood (RW).

Highlights

The differentiation of a vascular cambium and secondary tissues are amongst the most important events in the evolution of higher plants and a prerequisite for the existence of woody trees
Other glycophosphotidyl inositol (GPI)-anchored proteins have been implicated in receptor-like kinase trafficking from within the cell to the plasma membrane, possibly as cofactors or chaperones for these receptors [126]. Considering their position in the plant cell and how microtubules and arabinogalactan proteins seem to communicate, it can be speculated that cortical microtubules and the cellulose synthase complex (CSC) might associate via AGPs; further work is needed to demonstrate the actual effects of AGP on cellulose deposition and microfibril orientation
The cytoskeleton plays an important role in determining CSC delivery sites during secondary cell wall (SCW) deposition, and, in xylary cells, it has been demonstrated to be critical for proper microfibril orientation

Summary

Introduction

The differentiation of a vascular cambium and secondary tissues are amongst the most important events in the evolution of higher plants and a prerequisite for the existence of woody trees. In the SCW, the differential angle of cellulose microfibrils with respect to the long axis of a cell—a feature known as microfibril angle (MFA)—is well documented. This is especially true in the S2 layer, the large middle layer in a usually three-layered SCW, in which MFA is the main determinant of cell architecture and mechanical properties of fibres and tracheids [7]. We reviewed aspects of the involvement of microtubules and actin filaments in secondary cell wall formation in xylary cells of woody trees and put forward a model of cellulose microfibril angle (MFA) determination in trees forming reaction wood (RW) as a response to gravitational stimulus

MFA as a Key Feature of SCW Formation

Cellulose Properties and the CSC

Cytoskeleton Roles in SCW Biosynthesis

Microtubules Guide the CSC and Play a Role in SCW Patterning

Molecular Control of MFA

Arabinogalactans

Tubulins

Other Cell Wall-Related Genes

A Molecular Model for MFA Alterations in Response to Gravitational Stimulus

Findings

Conclusions