title: In vivo dynamics and differential microtubule-binding activities of MAP65 proteins.
abstract: Plant cells produce different microtubule arrays that are essential for cell division and morphogenesis without equivalent in other eukaryotes. Microtubule-associated proteins influence the behavior of microtubules that is presumed to culminate into transitions from one array to another. We analyzed the microtubule-binding properties of three Arabidopsis (Arabidopsis thaliana) members, AtMAP65-1, AtMAP65-4, and AtMAP65-5, in live cells using laser scanning confocal microscopy. Depending on the overall organization of the cortical array, AtMAP65-1-GFP (green fluorescent protein) and AtMAP65-5-GFP associated with a subset of microtubules. In cells containing both coaligned and oblique microtubules, AtMAP65-1-GFP and AtMAP65-5-GFP tended to be associated with the coaligned microtubules. Cortical microtubules labeled with AtMAP65-1-GFP and AtMAP65-5-GFP appeared as thick bundles and showed more resistance to microtubule-destabilizing drugs. The polymerization rates of AtMAP65-1-GFP and AtMAP65-5-GFP microtubules were similar to those of tubulin-GFP marked microtubules but were different from AtEB1a-GFP, a microtubule plus-end-binding EB1-like protein that stimulated polymerization. By contrast, depolymerization rates of AtMAP65-1-GFP- and AtMAP65-5-GFP-labeled microtubules were reduced. AtMAP65-1-GFP associated with polymerizing microtubules within a bundle, and with fixed microtubule termini, suggesting that AtMAP65-1's function is to bundle and stabilize adjacent microtubules of the cortex. Polymerization within a bundle took place in either direction so that bundling occurred between parallel or antiparallel aligned microtubules. AtMAP65-4-GFP did not label cortical microtubules or the preprophase band, despite continuous expression driven by the 35S promoter, and its subcellular localization was restricted to microtubules that rearranged to form a spindle and the polar sides of the spindle proper. The expression of AtMAP65-4 peaked at mitosis, in agreement with a function related to spindle formation, whereas AtMAP65-1 and AtMAP65-5 were expressed throughout the cell cycle.
authors.affiliation: Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology, Ghent University, B-9052 Ghent, Belgium.
authors.forename: Daniël
authors.initials: D
authors.lastname: Van Damme
authors.forename: Kris
authors.initials: K
authors.lastname: Van Poucke
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Boutant
authors.forename: Christophe
authors.initials: C
authors.lastname: Ritzenthaler
authors.forename: Dirk
authors.initials: D
authors.lastname: Inzé
authors.forename: Danny
authors.initials: D
authors.lastname: Geelen
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D001549:Benzamides / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins; D018613:Microscopy, Confocal; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D008938:Mitosis / Q000502:physiology; D009578:Nitrobenzenes; D009946:Organothiophosphorus Compounds / Q000494:pharmacology; D030821:Plants, Genetically Modified; D011485:Protein Binding; D014026:Nicotiana; D015533:Transcriptional Activation / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D001549:Benzamides; C483461:EB1 protein, Arabidopsis; C492901:MAP65-1 protein, Arabidopsis; D008869:Microtubule-Associated Proteins; D009578:Nitrobenzenes; D009946:Organothiophosphorus Compounds; D049452:Green Fluorescent Proteins; C001059:pronamide; C017823:amiprophos methyl