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The genetic programming
cell polarity using mosses
The experimental tractability of mosses make them ideal
models to study the genetic regulation of plant development,
combining classical and molecular genetic analysis with
cell biological studies. Mosses provide excellent material
for the study of both the generation of a polarity in
a symmetrical cell, and the modification of existing
polarity in response to environmental inputs.
The generation of a polar axis is studied using moss
protoplasts which regenerate by polar outgrowth, to
form cell filaments. We have shown that polar axis generation
involves two processes. Alignment with respect to the
light source is determined first. Axis orientation,
- whether outgrowth occurs towards or away from the
light, - is fixed later. Alignment and orientation are
sensitive to different light conditions and we propose
that independent gradients are set up to determine axis
alignment and orientation.
We study the modification of existing polarity using
apical cells of protonemal filaments. These are sensitive
to both light direction and gravity, modifying the direction
of polar outgrowth in response to changes in light direction
or, if re-oriented, with respect to gravity. We have
shown by mutant analysis, that light direction is detected
by phytochrome, and that the response to gravity is
actively turned of in light, again by way of phytochrome.
We have isolated mutants in which the orientation of
the response to gravity is reversed, - they grow down
rather than up - , while retaining their ability to
align to gravity, as well as mutants that are severely
impaired in axis alignment. Genetic analysis of these
mutants has established that loss of sensitivity to
gravity and reversal of the orientation of the gravitropic
response are likely to result form mutations in a single
gene. A gene targeting programme is now in hand and
several potential tagged mutants with altered gravity
responses have been identified and are now being analysed.
For research in to targeted gene replacement, see Andrew
Cuming’s page.
Reviews on the moss system:
Cove, D.J. 2005. Physcomitrella
patens. Annual Review of Genetics 39,
339-358.
Cove, D.J., Bezanilla, M., Harries,
P. and Quatrano, R.S. 2006. Mosses as model systems
for the study of metabolism and development. Annual
Review of Plant Biology 57, 497-520.
Selected research publications:
Cove, D.J., Quatrano, R.S. &
Hartmann, E. 1996. The alignment of the axis
of asymmetry in regenerating protoplasts of the moss,
Ceratodon purpureus, is determined independently
of axis polarity. Development 122, 371 - 397.
Kamisugi, Y., Cuming. A.C., & Cove, D.J. 2005.
Parameters determining the efficiency of homologous
recombination mediated gene targeting in the moss Physcomitrella
patens. Nucleic Acid Research 33 (19),
e173.
Cove, D.J. and Quatrano, R.S. 2006. Agravitropic
mutants of the moss, Ceratodon purpureus, do
not complement mutants having a reversed gravitropic
response. Plant, Cell and Environment (in press)
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