Download Plant Cortical Microtubule Arrays: Recruitment

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IN BRIEF
Plant Cortical Microtubule Arrays: Recruitment Mechanisms in
Common with Centrosomes
Plant microtubules dynamically change configurations during growth and development,
acting in cell division, polarity, and expansion
(reviewed in Ehrhardt, 2008). In interphase
cells, microtubules form parallel arrays in
the plant cortex, the area just beneath the
plasma membrane; the orientation of these
arrays changes in different cell types, depending on cell growth and function. For
example, in the rapidly expanding cells of
the root tip, microtubule cortical arrays form
bands transverse to the axis of elongation
and assist in cell elongation. In mitotic cells,
microtubule arrays change dramatically,
forming a preprophase band that anticipates
the plane of cell division, and then a spindle
that segregates the chromosomes.
In animal cells, radial microtubule arrays,
such as the spindle, are organized from the
centrosome, which contains microtubulenucleating proteins, including g-tubulin. The
early finding that higher plants do not
contain centrosomes established a longstanding mystery of how plant cells nucleate
and organize microtubules independent of
centrosomes. The microtubule-nucleating
g-tubulin and a number of microtubuleassociated proteins are known to act in
plant microtubule organization, but more
factors remain to be identified. Drevensek
et al. (2012) use the Arabidopsis thaliana TONNEAU1 (TON1) protein, a homolog
of the human centrosome-associated protein FOP (FGFR1OP), to further probe
the microtubule-organizing apparatus
of plants. The authors identified TON1interacting proteins by yeast two-hybrid
analysis and found a common sequence
motif, the TON1 recruiting motif (TRM),
which defines a protein family that has 34
members in Arabidopsis. The TRM proteins
share specific sequence motifs but otherwise show substantial structural diversity.
Indeed, TRM1 is a microtubule-associated
protein (see figure), as are many other TRM
proteins, but some TRM family members
do not appear to associate with microtubules, suggesting a functional diversity that
derives from the observed structural diversity.
Further characterizing TRM1, the authors
found that it binds directly to microtubules
and mapped the TRM1 microtubule binding
domain. Although TON1 colocalizes with
microtubules, the authors found that it presumably does not directly bind microtubules
but instead is recruited by its interaction
with TRM1. Indeed, this interaction appears
to be conserved in human centrosomes,
where the CAP350 protein, which contains
the same conserved interaction motifs as
the TRM proteins, recruits FOP to the
centrosome. Moreover, the authors found
that Arabidopsis TON1 interacted with the
conserved motifs from human CAP350 in
a yeast two-hybrid assay. Thus, this work
has identified an intriguing superfamily of
proteins with diverse functions that remain
to be explored and found a commonality in
mechanisms of protein recruitment between
the plant cortical microtubule arrays and the
centrosome.
Jennifer Mach
Science Editor
[email protected]
REFERENCES
TRM1 colocalizes with microtubules. Green fluorescent protein (GFP)-TRM1 (left) localizes to cortical
microtubule arrays in petal epidermal cells. The GFP-TRM1 signal (red) colocalizes with the
microtubule marker mCherry-B-tubulin 6 (green) in the overlaid image (right). Bars ¼ 10 mm. (Reprinted
from Figures 4E and 4F of Drevensek et al. [2012].)
Drevensek, S., Goussot, M., Duroc, Y.,
Christodoulidou, A., Steyaert, S., Schaefer,
E., Duvernois, E., Grandjean, O., Vantard,
M., Bouchez, D., and Pastuglia, M. (2012).
The Arabidopsis TRM1–TON1 interaction
reveals a recruitment network common to
plant cortical microtubule arrays and eucaryotic centrosomes. Plant Cell 10.1105/
tpc.111.089748.
Ehrhardt, D.W. (2008). Straighten up and fly
right: Microtubule dynamics and organization
of non-centrosomal arrays in higher plants.
Curr. Opin. Cell Biol. 20: 107-116.
www.plantcell.org/cgi/doi/10.1105/tpc.112.240111
The Plant Cell Preview, www.aspb.org ã 2012 American Society of Plant Biologists. All rights reserved.
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Plant Cortical Microtubule Arrays: Recruitment Mechanisms in Common with Centrosomes
Jennifer Mach
Plant Cell; originally published online January 27, 2012;
DOI 10.1105/tpc.112.240111
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