Abstract
MOR1, the Arabidopsis thaliana homologue of the Xenopus microtubule-associated protein MAP215, is required for spatial organization of the acentrosomal microtubule arrays of plant cells. To determine how loss of MOR1 function affects microtubule dynamics, we compared various parameters of microtubule dynamics in the temperature-sensitive mor1-1 mutant at its permissive and restrictive temperatures, 21 degrees C and 31 degrees C, respectively. Dynamic events were tracked in live cells expressing either GFP-tagged beta-tubulin or the plus end tracking EB1. Microtubule growth and shrinkage velocities were both dramatically reduced in mor1-1 at 31 degrees C and the incidence and duration of pause events increased. Interestingly, the association of EB1 with microtubule plus ends was reduced in mor1-1 whereas side wall binding increased, suggesting that MOR1 influences the association of EB1 with microtubules either by modulating microtubule plus end structure or by interacting with EB1. Although mor1-1 microtubules grew and shrank more slowly than wild-type microtubules at 21 degrees C, the incidence of pause was not altered, suggesting that pause events, which occur more frequently at 31 degrees C, have a major detrimental role in the spatial organization of cortical microtubules. Extensive increases in microtubule dynamics in wild-type cells when shifted from 21 degrees C to 31 degrees C underline the importance of careful temperature control in live cell imaging.
Highlights
Microtubules are highly dynamic structures that undergo transitions between states of growth, shrinkage and pause
We sought to quantify the effects of the mor1-1 temperaturesensitive mutation on several parameters of microtubule dynamics using GFP reporter proteins in living epidermal cells of the first leaf
In mor1-1, both microtubule growth and shrinkage rates were significantly reduced compared with the wild type (P
Summary
Microtubules are highly dynamic structures that undergo transitions between states of growth, shrinkage and pause. Depolymerization is encouraged when GDP-bound subunits are exposed This model for microtubule dynamics is insufficient for the living cell, in which the complex dynamic properties of microtubules are regulated by the activity of microtubule-associated proteins. The MAP215 proteins [CKAP5 (or TOGp) in human, Msps in Drosophila, ZYG-9 in C. elegans, Stu in S. cerevisiae, Dis or Alp in S. pombe, CP224 in Dictyostelium, MOR1 in Arabidopsis] are perhaps the most ubiquitous and conserved of microtubuleassociated proteins. They are found in eukaryotic organisms from all kingdoms and appear to be essential for survival (Gard et al, 2004). MAP215 was first identified in Xenopus egg cytoplasmic extracts as a factor promoting the elongation and stability of microtubules (Gard and Kirchner, 1987) but a later screen isolated XMAP215 as a major microtubule-destabilizing factor (Shirasu-Hiza et al, 2003)
Sign-in/Register to view highlights & summary 
Paper version not known (
Free)
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call