Ectopic expression of a wood-abundant expansin PttEXPA1 promotes cell expansion in primary and secondary tissues in aspen |
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Authors: | Gray-Mitsumune Madoka Blomquist Kristina McQueen-Mason Simon Teeri Tuula T Sundberg Björn Mellerowicz Ewa J |
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Institution: | UmeåPlant Science Centre, Department of Forest Genetics and Plant Physiology, SE-90183 Umeå, Sweden;Royal Institute of Technology, School of Biotechnology, AlbaNova University Centre, SE-10691 Stockholm, Sweden;Department of Biology, University of York, PO Box 373, York YO10 5YW, UK |
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Abstract: | Expansins are primary agents inducing cell wall extension, and are therefore obvious targets in biotechnological applications aimed at the modification of cell size in plants. In trees, increased fibre length is a goal of both breeding and genetic engineering programmes. We used an α-expansin Ptt EXPA1 that is highly abundant in the wood-forming tissues of hybrid aspen ( Populus tremula L. × P. tremuloides Michx.) to evaluate its role in fibre elongation and wood cell development. Ptt EXPA1 belongs to Subfamily A of α-expansins that have conserved motifs at the N- and C-termini of the mature protein. When PttEXPA1 was over-expressed in aspen, an extract of the cell wall-bound proteins of the transgenic plants exhibited an increased expansin activity on cellulose–xyloglucan composites in vitro , indicating that Ptt EXPA1 is an active expansin. The transgenic lines exhibited increased stem internode elongation and leaf expansion, and larger cell sizes in the leaf epidermis, indicating that Ptt EXPA1 protein is capable of increasing the growth of these organs by enhancing cell wall expansion in planta . Wood cell development was also modified in the transgenic lines, but the effects were different for vessel elements and fibres, the two main cell types of aspen wood. Ptt EXPA1 stimulated fibre, but not vessel element, diameter growth, and marginally increased vessel element length, but did not affect fibre length. The observed differences in responsiveness to expansin of these cell types are discussed in the light of differences in their growth strategies and cell wall composition. |
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Keywords: | cell expansion expansin fibre length poplar Populus transgenic trees wood formation xylogenesis |
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