A role for katanin in plant cell division: Microtubule organization in dividing root cells of fra2 and lue1Arabidopsis thaliana mutants

Abstract

Severing of microtubules by katanin has proven to be crucial for cortical microtubule organization in elongating and differentiating plant cells. On the contrary, katanin is currently not considered essential during cell division in plants as it is in animals. However, defects in cell patterning have been observed in katanin mutants, implying a role for it in dividing plant cells. Therefore, microtubule organization was studied in detail by immunofluorescence in dividing root cells of fra2 and lue1 katanin mutants of Arabidopsis thaliana. In both, early preprophase bands consisted of poorly aligned microtubules, prophase spindles were multipolar, and the microtubules of expanding phragmoplasts were elongated, bended toward and connected to the surface of daughter nuclei. Accordingly, severing by katanin seems to be necessary for the proper organization of these microtubule arrays. In both fra2 and lue1, metaphase/anaphase spindles and initiating phragmoplasts exhibited typical organization. However, they were obliquely oriented more frequently than in the wild type. It is proposed that this oblique orientation may be due to prophase spindle multipolarity and results in a failure of the cell plate to follow the predetermined division plane, during cytokinesis, producing oblique cell walls in the roots of both mutants. It is therefore concluded that, like in animal cells, katanin is important for plant cell division, influencing the organization of several microtubule arrays. Moreover, failure in microtubule severing indirectly affects the orientation of the division plane.

Mitotic Spindle Assembly in Land Plants: Molecules and Mechanisms

“…In addition, katanin-mediated severing may affect MT length in some cell types [137]. MT flux is also observed within the phragmoplast, but the molecules responsible remain to be identified [138].…”

The rise and fall of the phragmoplast microtubule array

“…This would suggest that the primary site of MT depolymerization is at the distal minus ends. A potential factor that may contribute to MT disassembly is the severing factor katanin (KTN) because the KTN1/p60 subunit decorates phragmoplast MTs [47]. If the minus ends of phragmoplast MTs are stabilized by anchoring to cellular structures, katanin would sever MTs and release these MTs from the anchorage.…”

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

“…5c). Severing by p60-katanin is pivotal for the organization of microtubule arrays in interphase and mitotic [10, 11, 17–20] cells. However, it has been suggested that, although critical for cortical microtubule orientation in fast elongating cells, severing is not important in interphase meristematic cells, the microtubule pattern of which was described as random [21, 22].…”

“…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.…”

“…Roots of untreated wild-type, fra2 , lue1 and ktn1/2 seedlings were also prepared for transmission electron microscopy (TEM) as previously described [11]. In brief, root segments comprising the developmental root zones were fixed for 4 h in 3% (v/v) glutaraldehyde in 50 mM sodium cacodylate, pH 7, post-fixed in 1% (w/v) osmium tetroxide for 3 h, dehydrated in an acetone series and embedded in Spurr’s resin.…”