Unda Faride, Kim Hoon, Hefer Charles, Ralph John, Mansfield Shawn D
Department of Wood Science, University of British Columbia, Vancouver, BC, Canada.
Department of Biochemistry, University of Wisconsin, Madison, WI, USA.
Plant Biotechnol J. 2017 Jul;15(7):865-878. doi: 10.1111/pbi.12682. Epub 2017 Mar 4.
Galactinol synthase is a pivotal enzyme involved in the synthesis of the raffinose family of oligosaccharides (RFOs) that function as transport carbohydrates in the phloem, as storage compounds in sink tissues and as soluble metabolites that combat both abiotic and biotic stress in several plant species. Hybrid poplar (Populus alba × grandidentata) overexpressing the Arabidopsis thaliana GolS3 (AtGolS3) gene showed clear effects on development; the extreme overexpressing lines were stunted and had cell wall traits characteristic of tension wood, whereas lines with only moderate up-regulation grew normally and had moderately altered secondary cell wall composition and ultrastructure. Stem cross-sections of the developing xylem revealed a significant increase in the number of vessels, as well as the clear presence of a G-layer in the fibres. Furthermore, AtGolS3-OE lines possessed higher cellulose and lower lignin contents, an increase in cellulose crystallinity, and significantly altered hemicellulose-derived carbohydrates, notably manifested by their mannose and xylose contents. In addition, the transgenic plants displayed elevated xylem starch content. Transcriptome interrogation of the transgenic plants showed a significant up-regulation of genes involved in the synthesis of myo-inositol, along with genes involved in sucrose degradation. The results suggest that the overexpression of GolS and its product galactinol may serve as a molecular signal that initiates metabolic changes, culminating in a change in cell wall development and potentially the formation of tension wood.
棉子糖合成酶是参与棉子糖家族寡糖（RFOs）合成的关键酶，RFOs在韧皮部中作为运输碳水化合物，在库组织中作为储存化合物，以及在几种植物物种中作为对抗非生物和生物胁迫的可溶性代谢物发挥作用。过表达拟南芥GolS3（AtGolS3）基因的杂交杨树（Populus alba × grandidentata）对发育有明显影响；极度过表达的品系生长受阻，具有张力木特有的细胞壁特征，而仅适度上调的品系生长正常，次生细胞壁组成和超微结构有适度改变。发育中的木质部的茎横切面显示导管数量显著增加，并且纤维中明显存在G层。此外，AtGolS3过表达品系的纤维素含量较高，木质素含量较低，纤维素结晶度增加，半纤维素衍生的碳水化合物显著改变，尤其表现为甘露糖和木糖含量。此外，转基因植物的木质部淀粉含量升高。对转基因植物的转录组分析表明，参与肌醇合成的基因以及参与蔗糖降解的基因显著上调。结果表明，GolS及其产物棉子糖的过表达可能作为一种分子信号，启动代谢变化，最终导致细胞壁发育改变，并可能形成张力木。
