Plant and Cell Physiology Advance Access published online on May 15, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcm055
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Xyloglucan endo-transglycosylase (XET) functions in gelatinous layers of tension wood fibers in poplar - a glimpse into the mechanism of the balancing act of trees**
1 Department of Forest Genetics and Plant Physiology, Umea Plant Science Center, SLU, S901 83 Umea. E-mails: Veronica.Bourquin{at}genfys.slu.se, Bjorn.Sundberg{at}genfys.slu.se, ewa.mellerowicz{at}genfys.slu.se
2 present address: Nobuyuki Nishikubo, RIKEN Plant Science Center 1-7-22 Suehiro-cho Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan. E-mail : nobun{at}psc.riken.jp
3 present address: Tatsuya Awano, Laboratory of Tree Cell Biology, Division of Forest and Biomaterials Science, Graduate School of Agriculture, Kyoto University, 606-8502 Kyoto, Japan. E-mail: awanot{at}kais.kyoto-u.ac.jp
4 present address: Alicja Banasiak, Institute of Plant Biology, University of Wroclaw, Kanonia 6/8, 50-328, Wroclaw, Poland. E-mail: balicja{at}biol.uni.wroc.pl
5 Department of Biotechnology, Royal Insitute of Technology (KTH), S-106 91 Stockholm, Sweden. E-mails: ifm{at}omrb.pnpi.spb.ru, harry{at}biochem.kth.se, tuula{at}biochem.kth.se
6 Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu-Tokyo 183-8509, Japan. E-mail: funada{at}cc.tuat.ac.jp
7 Research Institute for Sustainable Humanosphere, Kyoto University, Kyoto 611-0011, Japan. E-mail: taka{at}rish.kyoto-u.ac.jp
Corresponding author: Dr. Ewa J. Mellerowicz. Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences (SLU), S901-83 Umea, Sweden. E-mail: ewa.mellerowicz{at}genfys.slu.se tel: 46 (0)90 786 8367, FAX: 46 (0)90-786 8165, http://www.upsc.se/emellerowicz.htm
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Abstract |
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Tension wood is a specialized tissue of deciduous trees that functions in bending woody stems to optimize their position in space. Tension wood fibers that develop on one side of the stem have an increased potency to shrink compared to fibers on the opposite side, thus creating a bending moment. It is believed that the gelatinous (G) cell wall layer containing almost pure cellulose of tension wood fibers is pivotal to their shrinking. By analyzing saccharide composition and linkage in isolated G-layers of poplar we found that they contain some matrix components in addition to cellulose, of which xyloglucan is the most abundant. Xyloglucan, xyloglucan endo-transglycosylase (XET) activity, and xyloglucan endo-transglycosylase/hydrolase (XTH) gene products were detected in developing G-layers by labeling using CCRC-M1 monoclonal antibody, in situ incorporation of XXXG-SR and the polyclonal antibody to poplar PttXET16-34, respectively, indicating that xyloglucan is incorporated to the G-layer during its development. Moreover, several XTH transcripts were altered and were generally upregulated in developing tension wood compared to normal wood. In mature G-fibers, XTH gene products were detected in the G-layers while the XET activity was evident in the adjacent S2 wall layer. We propose that XET activity is essential for G-fiber shrinking by repairing xyloglucan cross-links between G- and S2 layers and thus maintaining their contact. Surprisingly, XTH gene products and XET activity persisted in mature G-fibers for several years suggesting that the enzyme functions after cell death repairing the cross links as they are being broken during the shrinking process.
Keywords: gravity responses - wood formation - secondary wall - Populus - reaction wood - xylogenesis
*These authors contributed equally to this paper
**The nucleotide sequences reported in this paper have been submitted to GenBank under following accession numbers: XTH16-34, AF515607 [GenBank] ; XTH16-26, EF194046 [GenBank] ; XTH16-35, EF151160 [GenBank] ; XTH16-36, EF194050 [GenBank] ; XTH16-6, EF194049 [GenBank] ; XTH16-21, EF194058 [GenBank] ; XTH16-30, EF194057 [GenBank] ; XTH16-17, EF194056 [GenBank] ; XTH16-39, EF194055 [GenBank] ; XTH16-14, EF194054 [GenBank] ; XTH16-3, EF194053 [GenBank] ; XTH16-27, EF194052 [GenBank] ; XTH16-1, EF194048 [GenBank] ; XTH16-38, EF194047 [GenBank] ; XTH16-25, EF194051 [GenBank] ; XTH16-29, EF194045 [GenBank]
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