State Key Laboratory of Tree Genetics and Breeding, Northeast Forestry University, Harbin, 150040, Heilongjiang, People's Republic of China.
School of Forest Resource and Environmental Science, Michigan Technological University, Houghton, MI, 49931, USA.
Plant Mol Biol. 2019 Jun;100(3):215-230. doi: 10.1007/s11103-019-00850-w. Epub 2019 May 4.
Two homologs PsnSuSy1 and PsnSuSy2 from poplar played largely similar but little distinct roles in modulating sink strength, accelerating vegetative growth and modifying secondary growth of plant. Co-overexpression of them together resulted in small but perceptible additive effects. Sucrose synthase (SuSy) acts as a crucial determinant of sink strength by controlling the conversion of sucrose into UDP-glucose, which is not only the sole precursor for cellulose biosynthesis but also an extracellular signaling molecule for plants growth. Therefore, modification of SuSy activity in plants is of utmost importance. We have isolated two SuSy genes from poplar, PsnSuSy1 and PsnSuSy2, which were preferentially expressed in secondary xylem/phloem. To investigate their functions, T2 tobacco transgenic lines of PsnSuSy1 and PsnSuSy2 were generated and then crossed to generate PsnSuSy1/PsnSuSy2 dual overexpression transgenic lines. SuSy activities in all lines were significantly increased though PsnSuSy1/PsnSuSy2 lines only exhibited slightly higher SuSy activities than either PsnSuSy1 or PsnSuSy2 lines. The significantly increased fructose and glucose, engendered by augmented SuSy activities, caused the alternations of many physiological, biochemical measures and phenotypic traits that include accelerated vegetative growth, thickened secondary cell wall, and increased stem breaking force, accompanied with altered expression levels of related pathway genes. The correlation relationships between SuSy activities and many of these traits were statistically significant. However, differences of almost all traits among three types of transgenic lines were insignificant. These findings clearly demonstrated that PsnSuSy1 and PsnSuSy2 had similar but little distinct functions and insubstantial additive effects on modulating sink strength and affecting allocation of carbon elements among secondary cell wall components.
两个杨树同源物 PsnSuSy1 和 PsnSuSy2 在调节库强、加速营养生长和改变植物次生生长方面发挥了很大但略有不同的作用。它们的共过表达导致了微小但可察觉的累加效应。蔗糖合酶（SuSy）通过控制蔗糖转化为 UDP-葡萄糖来调节库强，UDP-葡萄糖不仅是纤维素生物合成的唯一前体，也是植物生长的细胞外信号分子。因此，修饰植物中的 SuSy 活性至关重要。我们从杨树中分离到两个 SuSy 基因，PsnSuSy1 和 PsnSuSy2，它们在次生木质部/韧皮部中优先表达。为了研究它们的功能，我们生成了 T2 烟草转基因株系的 PsnSuSy1 和 PsnSuSy2，然后将它们杂交生成 PsnSuSy1/PsnSuSy2 双过表达转基因株系。所有株系的 SuSy 活性都显著增加，尽管 PsnSuSy1/PsnSuSy2 株系的 SuSy 活性仅略高于 PsnSuSy1 或 PsnSuSy2 株系。由于 SuSy 活性的增加，导致果糖和葡萄糖的含量显著增加，从而导致许多生理生化指标和表型特征的改变，包括营养生长加速、次生细胞壁变厚、茎折断力增加，同时相关途径基因的表达水平也发生了改变。SuSy 活性与许多这些性状之间的相关性具有统计学意义。然而，三种类型的转基因株系之间的几乎所有性状差异都不显著。这些发现清楚地表明，PsnSuSy1 和 PsnSuSy2 在调节库强和影响次生细胞壁成分中碳元素分配方面具有相似但略有不同的功能和微不足道的累加效应。
