In vivo dynamics and differential microtubule-binding activities of MAP65 proteins

Plant Physiol. 2004 Dec;136(4):3956-67. doi: 10.1104/pp.104.051623. Epub 2004 Nov 19.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / chemistry
  • Arabidopsis Proteins / metabolism*
  • Benzamides / pharmacology
  • Gene Expression Regulation, Plant
  • Green Fluorescent Proteins
  • Microscopy, Confocal
  • Microtubule-Associated Proteins / metabolism*
  • Microtubules / drug effects
  • Microtubules / metabolism*
  • Mitosis / physiology
  • Nitrobenzenes
  • Organothiophosphorus Compounds / pharmacology
  • Plants, Genetically Modified
  • Protein Binding
  • Tobacco
  • Transcriptional Activation / physiology

Substances

  • Arabidopsis Proteins
  • Benzamides
  • EB1 protein, Arabidopsis
  • MAP65-1 protein, Arabidopsis
  • Microtubule-Associated Proteins
  • Nitrobenzenes
  • Organothiophosphorus Compounds
  • Green Fluorescent Proteins
  • pronamide
  • amiprophos methyl