The C-Terminal Variable Region Specifies the Dynamic Properties ofArabidopsisMicrotubule-Associated Protein MAP65 Isotypes

Abstract

The microtubule-associated protein, MAP65, is a member of a family of divergent microtubule-associated proteins from different organisms generally involved in maintaining the integrity of the central spindle in mitosis. The dicotyledon Arabidopsis thaliana and the monocotyledon rice (Oryza sativa) genomes contain 9 and 11 MAP65 genes, respectively. In this work, we show that the majority of these proteins fall into five phylogenetic clades, with the greatest variation between clades being in the C-terminal random coil domain. At least one Arabidopsis and one rice isotype is within each clade, indicating a functional specification for the C terminus. In At MAP65-1, the C-terminal domain is a microtubule binding region (MTB2) harboring the phosphorylation sites that control its activity. The At MAP65 isotypes show differential localization to microtubule arrays and promote microtubule polymerization with variable efficiency in a MTB2-dependent manner. In vivo studies demonstrate that the dynamics of the association and dissociation of different MAP65 isotypes with microtubules can vary up to 10-fold and that this correlates with their ability to promote microtubule polymerization. Our data demonstrate that the C-terminal variable region, MTB2, determines the dynamic properties of individual isotypes and suggest that slower turnover is conditional for more efficient microtubule polymerization.

The rise and fall of the phragmoplast microtubule array

“…Such a discrepancy could lead to the assumption that MT interdigitation is an ancient phenomenon in the phragmoplast which has been abandoned in somatic cells of higher plants. However, a number of MT-interacting factors like MAPs that bundle phragmoplast MTs, as well as the phragmoplast specific Kinesin-12 motors decorate the phragmoplast midzone exclusively and highlight bundlelike structures [20,21]. Thus it suggests that anti-parallel MT bundles have trespassed the phragmoplast midline, otherwise these proteins would not appear at that site.…”

“…In fact, three lines of evidence support that other MAP65 isoforms function redundantly with MAP65-3. A few other MAP65 isoforms decorate phragmoplast MTs with biases toward the midzone [21]. The loss of MAP65-1 or MAP65-2 enhances the growth defects in the map65-3 null mutant [23].…”

“…While MAP65-3 conspicuously decorates the phragmoplast midzone, other MAP65 proteins exhibit different localization patterns [21]. So how do different MAP65 isoforms acquire different localization patterns in the phragmoplast?…”

“…So how do different MAP65 isoforms acquire different localization patterns in the phragmoplast? These proteins show the greatest variations in their C-terminal regions, which define their affinity for MTs and ability in regulating MT polymerization [21]. While the function of MAP65-3 in the phragmoplast cannot be replaced by MAP65-1, artificially grafting the C-terminal domain of MAP65-3 enables MAP65-1 to localize to the phragmoplast midzone and acquire most if not all the function of MAP65-3 [24 ].…”

Preprophase band formation and cortical division zone establishment: RanGAP behaves differently from microtubules during their band formation

“…Next, we compared the location of MTs and MAP65, which is an MT-associated protein family whose isotypes have been found in the PPBs. [58][59][60][61][62] We used anti-BY2MAP65 53 which cross-reacted with a single band of the crude extract of onion root tips (Fig. 1C).…”