Overexpression of SiGolS3 Enhances Cold Tolerance in Broussonetia papyrifera by Promoting Raffinose Family Oligosaccharides (RFOs) Accumulation.
Galactinol synthase (GolS) is a key rate-limiting enzyme in the biosynthetic pathway of raffinose family oligosaccharides (RFOs), and plays a crucial role in plant responses to abiotic stresses such as low temperature. Saussurea involucrata, an alpine plant adapted to extreme habitats, serves as an ideal resource for mining unique and elite stress-tolerance genes. In this study, we isolated and cloned the SiGolS3 gene from S. involucrata, and performed heterologous overexpression and functional verification in Broussonetia papyrifera. Physiological and biochemical analyses revealed that SiGolS3 exerts its cold-tolerant function by promoting RFO accumulation, which in turn maintains cellular osmotic homeostasis, alleviates reactive oxygen species damage, preserves plasma membrane integrity under low-temperature stress, and synergistically promotes cold-responsive gene expression, ultimately enhancing freezing tolerance in transgenic B. papyrifera. This study advances understanding of alpine plant adaptation to extreme environments and offers a candidate gene for woody plant stress tolerance improvement.