A conserved role for kinesin-5 in plant mitosis

Abstract

The mitotic spindle of vascular plants is assembled and maintained by processes that remain poorly explored at a molecular level. Here, we report that AtKRP125c, one of four kinesin-5 motor proteins in arabidopsis, decorates microtubules throughout the cell cycle and appears to function in both interphase and mitosis. In a temperature-sensitive mutant, interphase cortical microtubules are disorganized at the restrictive temperature and mitotic spindles are massively disrupted, consistent with a defect in the stabilization of anti-parallel microtubules in the spindle midzone, as previously described in kinesin-5 mutants from animals and yeast. AtKRP125c introduced into mammalian epithelial cells by transfection decorates microtubules throughout the cell cycle but is unable to complement the loss of the endogenous kinesin-5 motor (Eg5). These results are among the first reports of any motor with a major role in anastral spindle structure in plants and demonstrate that the conservation of kinesin-5 motor function throughout eukaryotes extends to vascular plants.

Endogenous localizome identifies 43 mitotic kinesins in a plant cell

“…Frog Eg5 is enriched near the spindle pole by dynein-dependent transport (36), whereas fly Klp61F is uniformly localized on the spindle MTs in the S2 cell line or embryos (30,37). AtKRP125c (At kinesin 5-c), one of four Arabidopsis kinesin-5s, and tobacco TKRP125 are abundantly localized to all MT arrays throughout the cell cycle (33,38). Despite the diverse localization pattern, the dominant concept regarding the general function of kinesin-5 is that it slides apart antiparallel MTs at the spindle midzone, because this can best explain its depletion phenotype in many cell types: spindle monopolarization (39)(40)(41).…”

Emerging molecular mechanisms that power and regulate the anastral mitotic spindle of flowering plants

“…and T.I.B., unpublished data) whereas the mutated allele of AtKIN5c (rsw7) severely compromises mitosis (Fig. 2) [Bannigan et al, 2007]. Interestingly, for AtKIN5d, there are apparently no available alleles with an insertion in an exon, suggesting that AtKIN5d is essential, conceivably forming a hetero-tetramer with AtKIN5c.…”

“…Recently, a kinesin-5 in arabidopsis was shown to have a critical role in mitotic spindle function, demonstrating conservation of function between animal and plant kinesin-5 proteins [Bannigan et al, 2007]. The temperature-sensitive mutant radially swollen 7 (rsw7); [Weidemeier et al, 2002] contains a point mutation in the motor domain of the kinesin-5 gene, AtKRP125c, and exhibits massive spindle deformities, reminiscent of those seen in animal and fungal cells with compromised kinesin-5 function (Fig.…”

“…Also, antibodies against the carrot homologue, DcKRP120-2 label the spindle and phragmoplast, accumulating particularly at the phragmoplast midline [Barrosso et al, 2000]. Surprisingly, in arabidopsis, AtKRP125c-GFP, expressed under its native promoter, is distributed along the entire length of microtubules in all arrays throughout the cell cycle and is neither restricted to the spindle nor enriched at the midzone [Bannigan et al, 2007]. The different localizations for plant kinesin-5 motor proteins may reflect the radiation that this clade has undergone in plants (see next section) and the attendant specialization.…”

“…In mammalian cells, phosphorylation is required to specifically target kinesin-5 (Eg5) to the spindle [Blangy et al, 1995;Sawin and Mitchison, 1995]. Although in plants, AtKIN5c appears to be localized to microtubules throughout the cell cycle [Bannigan et al, 2007], its activity at the spindle midzone could be regulated specifically by phosphorylation. In tobacco, the M-phase cyclin-dependent kinase localizes to the spindle midzone [Weingartner et al, 2001], most likely interacting with its targets, including MAP65 [Mao et al, 2005;Smertenko et al, 2006] and TKRP125 [Barroso et al, 2000].…”