A Katanin-like Protein Regulates Normal Cell Wall gBiosynthesis and Cell Elongation

Abstract

Fibers are one of the mechanical tissues that provide structural support to the plant body. To understand how the normal mechanical strength of fibers is regulated, we isolated an Arabidopsis fragile fiber ( fra2 ) mutant defective in the mechanical strength of interfascicular fibers in the inflorescence stems. Anatomical and chemical analyses showed that the fra2 mutation caused a reduction in fiber cell length and wall thickness, a decrease in cellulose and hemicellulose contents, and an increase in lignin condensation, indicating that the fragile fiber phenotype of fra2 is a result of alterations in fiber cell elongation and cell wall biosynthesis. In addition to the effects on fibers, the fra2 mutation resulted in a remarkable reduction in cell length and an increase in cell width in all organs, which led to a global alteration in plant morphology. The FRA2 gene was shown to encode a protein with high similarity to katanin (hence FRA2 was renamed AtKTN1 ), a protein shown to be involved in regulating microtubule disassembly by severing microtubules. Consistent with the putative function of AtKTN1 as a microtubule-severing protein, immunolocalization demonstrated that the fra2 mutation caused delays in the disappearance of perinuclear microtubule array and in the establishment of transverse cortical microtubule array in interphase and elongating cells. Together, these results suggest that AtKTN1, a katanin-like protein, is essential not only for normal cell wall biosynthesis and cell elongation in fiber cells but also for cell expansion in all organs.

KATANIN 1 Is Essential for Embryogenesis and Seed Formation in Arabidopsis

“…The ability to accurately control microtubule number, the rate of microtubule assembly and disassembly, and the assembly of microtubule networks governs cellular processes including differentiation, division and migration. A major regulatory mechanism of dynamic microtubule turnover in eukaryotes, involves microtubule severing by means of AAA-ATPase family proteins including katanin (McNally and Vale, 1993; Burk et al, 2001), fidgetin (Mukherjee et al, 2012) and spastin (Roll-Mecak and Vale, 2005). In plants as represented by the genetically tractable model Arabidopsis thaliana , only katanin has been identified as a microtubule severing protein (Burk et al, 2001; McClinton et al, 2001), and was shown thereon to play central roles in mechanisms governing microtubule organization.…”

Cortical microtubule orientation in Arabidopsis thaliana root meristematic zone depends on cell division and requires severing by katanin

“…Furthermore, our data support that microtubule severing is required for transverse microtubule orientation since its initiation in the meristematic cells. Importantly, random microtubule orientation in p60-katanin mutants results in decreased cell length in the fast elongation zone [7, 21] as well as in the meristematic zone [11]. Accordingly, microtubule severing is required throughout all the developmental zones of A. thaliana root, for both the establishment and maintenance of the transverse pattern that underlies anisotropic expansion.…”

“…Cortical microtubule organization was studied in wild-type A. thaliana primary roots, in which cells stopped dividing after treatment with aphidicolin, a potent inhibitor of DNA replication [6]. In addition, in order to further investigate the factors involved in microtubule orientation, we compared cortical microtubule arrangement in meristematic root cells of the wild-type and of the p60-katanin mutants fra2 [7], lue1 [8] and ktn1/2 [9]. Our findings support that establishment of transverse cortical microtubule orientation in the meristematic zone of A. thaliana root is substantially associated to cell division and depends on microtubule severing.…”

TOPOISOMERASE 6B is involved in chromatin remodelling associated with control of carbon partitioning into secondary metabolites and cell walls, and epidermal morphogenesis in Arabidopsis

“…in cell wall mutants). Some dwarf mutants ectopically deposit callose (Lukowitz et al , 2001), pectin (His et al , 2001), and the phenolic polymers suberin (Cheng et al , 2000) and lignin (Burk et al , 2001), thereby compromising the stability and flexibility of the cell wall. Treatment of wild-type plants with tunicamycin resulted in the appearance of patches of callose accumulation within the root elongation zone (Supplementary Fig.…”