Abstract
A goal of forest-tree biotechnology is to accelerate the growth and cellulose deposition of woody plants. Because the xyloglucan network suppresses elongation in higher plants, we expressed a xyloglucanase constitutively in Populus alba. The expression increased the lengths of stem and petiole and enlarged palisade parenchymal cells compacting in the limited space of the leaf. In stems, the secondary xylem fibers in transgenics had the same length as in controls but contained more cellulose. Increased stem growth was accompanied by a decreased Young's modulus in the growth zone, an increased Young's modulus in mature tissue, whereas cellulose deposition was enhanced in both regions. The results indicate that the degradation of the xyloglucan network could be a useful strategy for accelerating growth and cellulose content in forest trees.
