Improvement of wood quality is an important focus of forest genetics and breeding research. Sucrose synthase (SS) catalyzes the reaction of sucrose and uridine diphosphate into uridine diphosphate glucose and fructose. It is a key enzyme involved in cell wall formation during secondary growth by providing the UDP-Glucose substrate for cellulose biosynthesis. In this study, we isolated the single-copy gene PtSS3 from the SS gene family of Populus tomentosa and analyzed its structure. To identify its function in secondary growth, we generated 19 transgenic lines of P. tomentosa using PtSS3 overexpression (OE) and artificial microRNA (amiRNA) constructs. We also performed comprehensive analyses of the transgenic P. tomentosa plants, including phenotypic analyses, quantitative real-time PCR, enzyme activity assays and sugar metabolism. We found significantly higher PtSS3 enzyme activity, fructose, and glucose levels and significantly lower sucrose levels in the stems and leaves of OE-PtSS3 plants. The opposite trend was observed in the amiRNA-PtSS3 lines. Gene expression analyses showed that PtSS3 transcript levels in stems and leaves were up-regulated in the OE-PtSS3 lines and down-regulated in the amiRNA-PtSS3 lines, and the OE-PtSS3 plants grew taller than the wild-type and amiRNA-PtSS3 plants. These findings indicate that PtSS3 plays an important role in sucrose metabolism and growth of trees.

改善木材质量是森林遗传和育种研究的重要重点。蔗糖合酶（SS）催化蔗糖和尿苷二磷酸反应成尿苷二磷酸葡萄糖和果糖。通过为纤维素生物合成提供UDP-葡萄糖底物，它是在二次生长过程中参与细胞壁形成的关键酶。在这项研究中，我们从毛白杨的SS基因家族中分离了单拷贝基因PtSS3，并对其结构进行了分析。为了鉴定在二次生长其功能，我们产生的19个的转基因品系毛白杨使用PtSS3过度表达（OE）和人工microRNA（amiRNA）构建体。我们还对转基因毛白杨植株进行了综合分析，包括表型分析，定量实时PCR，酶活性测定和糖代谢。我们发现OE-PtSS3植物的茎和叶中PtSS3酶活性，果糖和葡萄糖水平明显更高，而蔗糖水平则显着降低。在amiRNA-PtSS3细胞系中观察到相反的趋势。基因表达分析表明PtSS3茎和叶中的转录本水平在OE-PtSS3系中被上调，而在amiRNA-PtSS3系中被下调，并且OE-PtSS3植物的生长比野生型和amiRNA-PtSS3的植物高。这些发现表明PtSS3在蔗糖代谢和树木生长中起重要作用。