Lab members
Dr Henrik Buschmann (Postdoctoral scientist)
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| Upper panel: GFP-AIR9 labels PPBs in adjacent cells, forecasting the plane of cell division. Lower panel: after mitosis GFP-AIR9 returnsto the former PPB sites as a torus (arrows) that moves inwards on the new dividing wall. |
Henrik previously investigated a novel, plant-specific microtubule-associated protein, TORTIFOLIA1/SPIRAL2 (Buschmann et al [2004] Current Biology).
The tor1 mutant grows in a twisted, helical fashion, showing that the protein is necessary for the plant to grow straight. Several proteins and drugs that affect microtubule behaviour are now known to affect whether plants grow with a right – or a left-handed helical twist and this is one of the group’s major interests.
Henrik has subsequently characterized another novel MAP, AIR9, discovered in our proteomic screen. AIR9 decorates cortical microtubules and also the preprophase band of microtubules (PPB) that forecasts the plane in which the cell is about to divide (Buschmann et al.,[2006]. Current Biol. 16, 1938-1943).
AIR9 disappears from the predicted site during mitosis
but returns just as the new dividing wall inserts into the parental
wall. AIR9 therefore appears to play a part in the ‘memorization’
of the division plane and we continue to investigate this.
Dr Edouard Pesquet (Postdoctoral scientist)
In his PhD and post-doctoral work, Edouard used the Zinnia elegans tracheary element (TE) differentiation system (ref 1) to study the role of gene expression and hormone responsiveness . The cytoskeleton is thought to be a key regulator of TE secondary cell wall formation since the bunching of microtubules seems to determine where the characteristic thickenings of secondary cellulose will be deposited, and later on lignin. Edouard’s aim is to develop a more amenable Arabidopsis TE differentiation system (figure 1) to describe the behaviour of microtubules during TE formation and to identify the microtubule associated proteins involved in differentiation.
Figure 1. Arabidopsis Col-0 TE differentiation system. A: undifferentiated
Col-0 cells, B: TE exhibiting a spiral secondary cell wall, C: TE exhibiting
a reticulate secondary cell wall. Bar= 8 µm.
Reference 1: (Pesquet et al. [2004] Plant J, [2005] Plant Physiol)
Dr Adrian Sambade Zumoffen (Postdoctoral scientist)
In his previous research, Adrian found evidence that microtubule dynamics support the intracellular localization and movement of viral RNA in N. benthamiana (1, 2). Microtubules in interphase plant cells have been seen to be associated with the plasma membrane, forming parallel groups or bundles. These groupings represent the basic building blocks of the cortical microtubule array. Recent studies in this laboratory (3) showed that over several hours bundles undergo rotary movements in Arabidopsis hypocotyl epidermal cells. Adrian is using this model to understand the role of the whole-cell microtubule array in cell elongation.
Fig.1: Microtubule bundles rotating over a three-hour
period in an Arabidopsis thaliana (Ler) hypocotyl epidermal cell expressing
fluorescently tagged EB1 protein.
Other work
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| Overexpression of GFP-AtMAP65-1 in Arabidopsis suspension cells draws cortical microtubules into helical bundles that resemble the helical patterns seen in xylem cells |
We previously showed that MAP65 is responsible for drawing microtubules into parallel groups in vitro by forming 25nm cross-bridges between them. A spectacular natural example of such microtubule bundling is shown when leaf mesophyll cells of the ornamental plant zinnia transdifferentiate into xylem cells when isolated in culture. The evenly-distributed cortical microtubules are drawn into helical and hooped bundles that act as templates for the characteristic wall thickenings. Guojie Mao ( Mao et al., [2006] J. Cell Science 119, 753-758) identified MAP65 isoforms involved in this differentiation in zinnia. In addition, he showed how this bundling activity is down-regulated by phosphorylation as Arabidopsis cells divide (Mao et al., [2005] Plant Journal 43, 469-478).
Clive Lloyd
John Innes Centre
Norwich Research Park,
Colney, Norwich NR4 7UH, UK
clive.lloyd@bbsrc.ac.uk
John Innes CentreNorwich Research Park,
Colney, Norwich NR4 7UH, UK
clive.lloyd@bbsrc.ac.uk