Broadly, I am interested in how
plant cells co-ordinate their growth with those around them to form a complex
multicellular organism, and how they co-ordinate responses to changes in
the environment.
Precise control over cell division and expansion is of fundamental
importance in plants, in part because cell migration is prevented by the
presence of cell a wall.
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Developmental events, such as the formation of a new organ
or the healing of a wound require not only careful control over division
and growth but, very often, a change in the orientation of these. Instances have been reported where cortical microtubules,
the filamentous protein polymers that are believed to influence the direction
of cell growth by guiding cellulose deposition, realign into complex arrays
that transcend cell boundaries and predict the new axis of growth. These intercellular patterns in microtubule alignment
have been commented on by several authors, but not investigated specifically.
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examples of microtubules apparently aligned between cells. Photo
courtesy Debbie Barton. |
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How is information shared between cells to allow the co-ordination
of intercellular microtubule organisation? My PhD project
tested the hypothesis that a signal is transmitted between cells via
the plasmodesmata (the tiny channels that connect plant cells to each other,
allowing transport and communication between cells) that aligns microtubules
in neighbouring cells.
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microtubules in rsw6 are arranged in parallel arrays within cells,
but not aligned with those in cells around them. |
To investigate this, I used a temperature-sensitive microtubule
mutant of arabidopsis, rsw6, in which microtubules are organised
within individual cells but do not align with those in adjoining cells, as
microtubules in wild type cells do. The mutant looks as though "local"
or cellular microtubule organisation is fine, but that "regional", or trans-cellular
microtubule organisation is somehow deficient. [1]
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I used a combination of microinjection of fluorescent tracers
- to show cell-to-cell transport - and immunofluorescent labelling of microtubules
to make correlations between the organisation of microtubules and the level
of cell-to-cell communication in this mutant.
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These studies revealed that microtubule reorientation precedes
a reduction in cell-to-cell communication. Microtubule
misalignment is reversible with transfer back to the permissive temperature,
as is the reduction in intercellular transport.
Also, I found that if a plant was treated with the microtubule-stabilising
drug taxol before it was transferred to 30oC, the microtubules were prevented
from reorienting. What's more, these plants did not lose intercellular communication
like plants with misaligned microtubules did, even though they were at 30oC
as well.
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movement of fluorescent dye between cells shows the level of cell-cell communication.
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Currently, I am working on identifying the rsw6 gene, in the hope that it will help
us to understand how microtubules get organized, and how their organization
is co-ordinated across many cells.
At the same time, I am studying the microtubule dynamics in
rsw6 using GFP-tubulin
rsw6 lines. This
allows us to see how microtubules look and behave in living plants, rather
than in fixed material
References:
[1] Bannigan, A.; Wiedemeier, A.M.D.; Williamson, R.E.; Overall, R. (2006) Cortical Microtubule Arrays Lose Uniform Alignment between Cells and Are Oryzalin Resistant in the Arabidopsis Mutant, radially swollen 6. Plant & Cell Physiology 47(7) |
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