First published online September 20, 2007; 10.1104/pp.107.107086
Plant Physiology 145:961-973 (2007)
© 2007 American Society of Plant Biologists
OPEN ACCESS ARTICLE
SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION
Differential Expansion and Expression of  - and  -Tubulin Gene Families in Populus1,[W],[OA]
Rodney V. Oakley,
Yuh-Shuh Wang2,
Wusirika Ramakrishna,
Scott A. Harding and
Chung-Jui Tsai*
Biotechnology Research Center, School of Forest Resources and Environmental Science (R.V.O., Y.-S.W., S.A.H., C.-J.T.), and Department of Biological Sciences (W.R.), Michigan Technological University, Houghton, Michigan 49931; and Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401 (Y.-S.W.)
Microtubule organization is intimately associated with cellulose microfibril deposition, central to plant secondary cell wall development. We have determined that a relatively large suite of eight  -TUBULIN (TUA) and 20  -TUBULIN (TUB) genes is expressed in the woody perennial Populus. A number of features, including gene number, : gene representation, amino acid changes at the C terminus, and transcript abundance in wood-forming tissue, distinguish the Populus tubulin suite from that of Arabidopsis thaliana. Five of the eight Populus TUAs are unusual in that they contain a C-terminal methionine, glutamic acid, or glutamine, instead of the more typical, and potentially regulatory, C-terminal tyrosine. Both C-terminal Y-type (TUA1) and M-type (TUA5) TUAs were highly expressed in wood-forming tissues and pollen, while the Y-type TUA6 and TUA8 were abundant only in pollen. Transcripts of the disproportionately expanded TUB family were present at comparatively low levels, with phylogenetically distinct classes predominating in xylem and pollen. When tension wood induction was used as a model system to examine changes in tubulin gene expression under conditions of augmented cellulose deposition, xylem-abundant TUA and TUB genes were up-regulated. Immunolocalization of TUA and TUB in xylem and phloem fibers of stems further supported the notion of heavy microtubule involvement during cellulose microfibril deposition in secondary walls. The high degree of sequence diversity, differential expansion, and differential regulation of Populus TUA and TUB families may confer flexibility in cell wall formation that is of adaptive significance to the woody perennial growth habit.
1 This work was supported by the U.S. Department of Agriculture National Research Initiative (grant nos. 98–35106–6630 to C.-J.T., 2003–35103–12906 to C.-J.T. and S.A.H., and 2005–35103–15251 to C.-J.T.).
2 Present address: Institute of Technology, University of Tartu, Nooruse St 1, 50411 Tartu, Estonia.
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Chung-Jui Tsai (chtsai{at}mtu.edu).
[W] The online version of this article contains Web-only data.
[OA] Open Access articles can be viewed online without a subscription.
www.plantphysiol.org/cgi/doi/10.1104/pp.107.107086
* Corresponding author; e-mail chtsai{at}mtu.edu.
Received August 8, 2007;
accepted September 17, 2007;
published September 20, 2007.
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