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The role of microtubule binding proteins and post-translational modifications of tubulin during plant vessel formation in Arabidopsis
Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
2015 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

In vascular plants, xylem tracheary elements (TEs) form the conducting tubes responsible for the hydro-mineral sap distribution between roots and leaves. Besides their role in sap transport, they also strengthen plant stems allowing upward growth of plants on land. TEs enable plants to resist mechanical constrains by laying down a thick lateral patterned secondary cell wall. The deposition of secondary cell wall material in TEs is strictly controlled by the underlying network of cortical microtubules. Such a microtubular network is a highly dynamic structure that organizes the content of the cell by anchoring or moving cellular components. The dynamic instability of the microtubules is controlled by three main factors. First, the amount of tubulin; the basic building blocks of microtubules, which are necessary for the microtubular assembly or disassembly. Second, microtubule associated proteins (MAPs), proteins capable of binding microtubules, which control microtubule stability and organization. Third, the cytoplasmic energy in GTP levels which regulate the energy dependent assembly of microtubules.

In this research project we try to decipher if secondary cell wall patterning in TEs is achieved to a process of local microtubule stabilization or destabilization. To accomplish this, we investigated variations in tubulin quantities during TE differentiation in Arabidopsis cell cultures. Our data shows that fluctuation in tubulin levels during TE differentiation are not correlated to the process of secondary cell wall formation. In addition, we investigated how the microtubular state changes between undifferentiating and differentiating cell cultures. Using a new protocol we were able to show that differentiating TEs are enriched with stable microtubules. Since the increase in stability is not correlated to increasing tubulin amounts, other factors such as TE-specific MAPs and post-translational modifications (PTMs) of tubulin, have been investigated.

Because such PTMs could act as molecular beacons, modifying the properties and behaviour of microtubules or its interacting MAPs, we investigated changes in tubulin-tyrosination during TE differentiation. Our experiments show a positive correlation between tubulin-tyrosination, secondary cell wall formation and the amount of available tubulin. This suggest that the tyrosination of tubulin might act as a signal for microtubular stabilization.

Furthermore we evaluated the effect of xylem-specific MAPs on TE patterning in planta. Using tDNA mutants of MAP70-5 and MIDD1, respectively stabilizing and destabilizing MAPs, we were able to show that TE secondary cell wall patterning is mainly determined by microtubular stabilization rather than destabilization.

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Biochemistry and Molecular Biology
URN: urn:nbn:se:umu:diva-111065OAI: diva2:871782
Available from: 2015-12-22 Created: 2015-11-03 Last updated: 2015-12-22Bibliographically approved

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Department of Plant PhysiologyUmeå Plant Science Centre (UPSC)
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