Coleman Heather D, Yan Jimmy, Mansfield Shawn D
Department of Wood Science, University of British Columbia, Vancouver, BC, Canada V6T 1Z4.
Proc Natl Acad Sci U S A. 2009 Aug 4;106(31):13118-23. doi: 10.1073/pnas.0900188106. Epub 2009 Jul 22.
Overexpression of the Gossypium hirsutum sucrose synthase (SuSy) gene under the control of 2 promoters was examined in hybrid poplar (Populus alba x grandidentata). Analysis of RNA transcript abundance, enzyme activity, cell wall composition, and soluble carbohydrates revealed significant changes in the transgenic lines. All lines showed significantly increased SuSy enzyme activity in developing xylem. This activity manifested in altered secondary cell wall cellulose content per dry weight in all lines, with increases of 2% to 6% over control levels, without influencing plant growth. The elevated concentration of cellulose was associated with an increase in cell wall crystallinity but did not alter secondary wall microfibril angle. This finding suggests that the observed increase in crystallinity is a function of altered carbon partitioning to cellulose biosynthesis rather than the result of tension wood formation. Furthermore, the augmented deposition of cellulose in the transgenic lines resulted in thicker xylem secondary cell wall and consequently improved wood density. These findings clearly implicate SuSy as a key regulator of sink strength in poplar trees and demonstrate the tight association of SuSy with cellulose synthesis and secondary wall formation.
在杂交杨树（银白杨×大齿杨）中检测了在2种启动子控制下的陆地棉蔗糖合酶（SuSy）基因的过表达情况。对RNA转录丰度、酶活性、细胞壁组成和可溶性碳水化合物的分析表明，转基因株系发生了显著变化。所有株系在发育中的木质部中均表现出蔗糖合酶活性显著增加。这种活性表现为所有株系中每干重的次生细胞壁纤维素含量发生改变，比对照水平增加了2%至6%，且不影响植物生长。纤维素浓度的升高与细胞壁结晶度的增加相关，但未改变次生壁微纤丝角。这一发现表明，观察到的结晶度增加是碳分配改变以促进纤维素生物合成的结果，而非张力木形成的结果。此外，转基因株系中纤维素沉积的增加导致木质部次生细胞壁变厚，从而提高了木材密度。这些发现清楚地表明蔗糖合酶是杨树库强度的关键调节因子，并证明了蔗糖合酶与纤维素合成和次生壁形成的紧密关联。
