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Functions of Xyloglucan in Plant Cells

Molecular Plant 2011年第1期4卷 17-24页

作者： Takahisa Hayashi Rumi Kaida Department of Bioscience Tokyo University of Agriculture I-I-I Sakuragaoka Setagaya-ku Tokyo 156-8502 Japan

While an increase in the number of xyloglucan tethers between the cellulose microfibrils in plant cell walls increases the walls＇ rigidity, the degradation of these tethers causes the walls to loosen. Degradation can occur either through the integration of xyloglucan oligosaccharides due to the action of xyloglucan endotransglucosylase or through direct hydrolysis due to the action of xyloglucanase. This is why the addition of xyloglucan and its fragment oligosac- charides causes plant tissue tension to increase and decrease so dramatically. Experiments involving the overexpression of xyloglucanase and cellulase have revealed the roles of xyloglucans in the walls. The degradation of wall xyloglucan in poplar by the transgenic expression of xyloglucanase, for example, not only accelerated stem elongation in the primary wall, but also blocked upright-stem gravitropism in the secondary wall. Overexpression of cellulase also reduced xylo- glucan content in the walls as cellulose microfibrils were trimmed at their amorphous region, resulting in increased cell volume in Arabidopsis leaves and in sengon with disturbed leaf movements. The hemiceflulose xylogiucan, in its function as a tether, plays a key role in the loosening and tightening of cellulose microfibrils： it enables the cell to change its shape in growth and differentiation zones and to retain its final shape after cell maturation.

关键词： Cellulose microfibrils cellulase plant growth xyloglucan xyloglucanase.

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Loosening Xyloglucan Accelerates the Enzymatic Degradation of Cellulose in Wood

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Molecular Plant 2009年第5期2卷 904-909页

作者： Rumi Kaida Tomomi Kaku Kei'ichi Baba Masafumi Oyadomari Takashi Watanabe Koji Nishida Toshiji Kanaya Ziv Shani Oded Shoseyov Takahisa Hayashi Kyoto University RISH Gokasho Uji Kyoto 611-0011 Japan Kyoto University Institute for Chemical Research Gokasho Uji Kyoto 611-0011 Japan CBD Technologies Rehovot 76100 Israel Institute of Sustainability Science Kyoto University Gokasho Uji Kyoto 611-0011 Japan

In order to create trees in which cellulose, the most abundant component in biomass, can be enzymatically hydrolyzed highly for the production of bioethanol, we examined the saccharification of xylem from several transgenic poplars, each overexpressing either xyloglucanase, cellulase, xylanase, or galactanase. The level of cellulose degradation achieved by a cellulase preparation was markedly greater in the xylem overexpressing xyloglucanase and much greater in the xylems overexpressing xylanase and cellulase than in the xylem of the wild-type plant. Although a high degree of degradation occurred in all xylems at all loci, the crystalline region of the cellulose microfibrUs was highly degraded in the xylem overexpressing xyloglucanase. Since the complex between microfibrils and xyloglucans could be one region that is particularly resistant to cellulose degradation, loosening xyloglucan could facilitate the enzymatic hydrolysis of cellulose in wood.

关键词： Overexpression of xyloglucanase saccharification transgenic poplar xylem.

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Xyloglucan for Generating Tensile Stress to Bend Tree Stem

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Molecular Plant 2009年第5期2卷 893-903页

作者： Kei'ichi Baba Yong Woo Park Tomomi Kaku Rumi Kaida Miyuki Takeuchi Masato Yoshida Yoshihiro Hosoo Yasuhisa Ojio Takashi Okuyama Toru Taniguchi Yasunori Ohmiya Teiji Kondo Ziv Shani Oded Shoseyov Tatsuya Awano Satoshi Serada Naoko Norioka Shigemi Norioka Takahisa Hayashi Kyoto University RISH Gokasho Uji Kyoto 611-0011 Japan Graduate School of Bioagricultural-Sciences Nagoya University Nagoya 464-8601 Japan Forest Tree Breeding Center Hitachi Ibaraki 319-1301 Japan CBD Technologies Rehovot 76100 Israel Division of Forest and Biomaterials Science Kyoto University Kyoto 606-8502 Japan Graduate School of Frontier Biosciences Osaka University Suita Osaka 565-0871 Japan Institute of Sustainability Science Kyoto University Gokasho Uji Kyoto 611-0011 Japan

In response to environmental variation, angiosperm trees bend their stems by forming tension wood, which consists of a cellulose-rich G （gelatinous）-Iayer 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 micro fibrils.

关键词： G-layer tensile stress xyloglucan xyloglucan endotransglucosylase

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