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Molecular Plant Advance Access originally published online on July 28, 2009
Molecular Plant 2009 2(5):893-903; doi:10.1093/mp/ssp054
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© The Author 2009. Published by the Molecular Plant Shanghai Editorial Office in association with Oxford University Press on behalf of CSPP and IPPE, SIBS, CAS.

Xyloglucan for Generating Tensile Stress to Bend Tree Stem

Kei'ichi Babaa, Yong Woo Parka, Tomomi Kakua, Rumi Kaidaa, Miyuki Takeuchia, Masato Yoshidab, Yoshihiro Hosoob, Yasuhisa Ojiob, Takashi Okuyamab, Toru Taniguchic, Yasunori Ohmiyac, Teiji Kondoc, Ziv Shanid, Oded Shoseyovd, Tatsuya Awanoe, Satoshi Seradaf, Naoko Noriokaf, Shigemi Noriokaf and Takahisa Hayashia,g,1

a Kyoto University, RISH, Gokasho, Uji, Kyoto 611-0011, Japan
b Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
c Forest Tree Breeding Center, Hitachi, Ibaraki 319-1301, Japan
d CBD Technologies, Rehovot 76100, Israel
e Division of Forest and Biomaterials Science, Kyoto University, Kyoto 606-8502, Japan
f Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan
g Institute of Sustainability Science, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan

1 To whom correspondence should be addressed. E-mail taka{at}rish.kyoto-u.ac.jp, fax and tel. +81 774 38 3618.

In response to environmental variation, angiosperm trees bend their stems by forming tension wood, which consists of a cellulose-rich G (gelatinous)-layer in the walls of fiber cells and generates abnormal tensile stress in the secondary xylem. We produced transgenic poplar plants overexpressing several endoglycanases to reduce each specific polysaccharide in the cell wall, as the secondary xylem consists of primary and secondary wall layers. When placed horizontally, the basal regions of stems of transgenic poplars overexpressing xyloglucanase alone could not bend upward due to low strain in the tension side of the xylem. In the wild-type plants, xyloglucan was found in the inner surface of G-layers during multiple layering. In situ xyloglucan endotransglucosylase (XET) activity showed that the incorporation of whole xyloglucan, potentially for wall tightening, began at the inner surface layers S1 and S2 and was retained throughout G-layer development, while the incorporation of xyloglucan heptasaccharide (XXXG) for wall loosening occurred in the primary wall of the expanding zone. We propose that the xyloglucan network is reinforced by XET to form a further connection between wall-bound and secreted xyloglucans in order to withstand the tensile stress created within the cellulose G-layer microfibrils.

Key Words: G-layer • tensile stress • xyloglucan • xyloglucan endotransglucosylase


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