Manipulation of the Expression of <i>SNAT1</i> Enhances Melatonin Biosynthesis, Promotes Plant Growth, and Improves Salt Stress Tolerance in Kiwifruit

Kiwifruit is susceptible to salt stress due to its shallow root system. Melatonin has been demonstrated to play a crucial role in responding to abiotic stresses, particularly salinity stress. In this study, we isolated a key melatonin biosynthesis gene, PavSNAT1, from sweet cherry and generated transgenic kiwifruit plants overexpressing PavSNAT1. The transgenic plants exhibited increased melatonin and cytokinin levels, accompanied by improved growth performance. Under salt stress conditions, transgenic plants demonstrated enhanced tolerance by alleviating ROS accumulation and chlorophyll degradation and increasing free amino acid content. Furthermore, three salt-responsive transcription factors, AcMYB60, AcBZIP11, and AcERF8, were highly upregulated under salt stress in transgenic plants. Transient overexpression of these genes resulted in enhanced salt tolerance in kiwifruit. Collectively, our findings demonstrate that heterologous expression of PavSNAT1 enhances plant growth and salt stress resistance in kiwifruit, revealing a promising strategy for improving crop resilience under adverse environmental conditions.