Alteration of Oriented Deposition of Cellulose Microfibrils by Mutation of a Katanin-Like Microtubule-Severing Protein

Abstract

It has long been hypothesized that cortical microtubules (MTs) control the orientation of cellulose microfibril deposition, but no mutants with alterations of MT orientation have been shown to affect this process. We have shown previously that in Arabidopsis, the fra2 mutation causes aberrant cortical MT orientation and reduced cell elongation, and the gene responsible for the fra2 mutation encodes a katanin-like protein. In this study, using field emission scanning electron microscopy, we found that the fra2 mutation altered the normal orientation of cellulose microfibrils in walls of expanding cells. Although cellulose microfibrils in walls of wild-type cells were oriented transversely along the elongation axis, cellulose microfibrils in walls of fra2 cells often formed bands and ran in different directions. The fra2 mutation also caused aberrant deposition of cellulose microfibrils in secondary walls of fiber cells. The aberrant orientation of cellulose microfibrils was shown to be correlated with disorganized cortical MTs in several cell types examined. In addition, the thickness of both primary and secondary cell walls was reduced significantly in the fra2 mutant. These results indicate that the katanin-like protein is essential for oriented cellulose microfibril deposition and normal cell wall biosynthesis. We further demonstrated that the Arabidopsis katanin-like protein possessed MT-severing activity in vitro; thus, it is an ortholog of animal katanin. We propose that the aberrant MT orientation caused by the mutation of katanin results in the distorted deposition of cellulose microfibrils, which in turn leads to a defect in cell elongation. These findings strongly support the hypothesis that cortical MTs regulate the oriented deposition of cellulose microfibrils that determines the direction of cell elongation.

Helical Microtubule Arrays and Spiral Growth

“…In the previous issue of The Plant Cell , Burk and Ye (2002) used a combination of field emission scanning electron microscopy (to study the wall) and immunofluorescence (to study the microtubules). They were able to demonstrate that the disorganized microtubules of the katanin mutant fra2 correlated with the loss of oriented cellulose deposition in primary and secondary cell walls and with the formation of abnormal bundles of cellulose.…”

“…They were able to demonstrate that the disorganized microtubules of the katanin mutant fra2 correlated with the loss of oriented cellulose deposition in primary and secondary cell walls and with the formation of abnormal bundles of cellulose. The use of mutants as genetic tools is more selective than the use of antimicrotubule herbicides, which are challenged as having unpredicted side effects, and these results were suggested to support a direct role for microtubules in controlling wall organization (Burk and Ye, 2002).…”

A Kinesin-Like Protein Is Essential for Oriented Deposition of Cellulose Microfibrils and Cell Wall Strength

“…Except for a few cases in which no parallel alignment of cortical microtubules and cellulose microfibrils is found (Preston, 1988;Emons et al, 1992;Wasteneys, 2000), the correlative alignment of cortical microtubules and cellulose microfibrils has been demonstrated in both elongating cells and cells undergoing secondary wall thickening, such as tracheary elements and fiber cells (Baskin, 2001). Recently, it was shown that an alteration in cortical microtubule orientation caused by mutation of the katanin-like microtubule-severing protein AtKTN1 in the fragile fiber2 ( fra2 ) mutant accompanies the aberrant deposition of cellulose microfibrils in the primary walls of elongating cells and the secondary walls of fiber cells Burk and Ye, 2002), which further supports the idea of microtubule/microfibril parallelism.…”

Knockout of the AtCESA2 Gene Affects Microtubule Orientation and Causes Abnormal Cell Expansion in Arabidopsis

“…Hypothetically, the cortical microtubules control the orientation of cellulose microfibril deposition. Burk and Ye (2002) proposed that the aberrant microtubule orientation caused by a mutation in katanin, a microtubule-severing protein, results in the distorted deposition of cellulose microfibrils, which, in turn, leads to a defect in cell elongation. But the reports from Wasteneys' lab led to serious questioning of the consensus model on microtubule regulation of microfibril orientation.…”