AcCHI, a Chitinase from Atriplex canescens, Confers Enhanced Tolerance to Osmotic and Salt Stress in Glycine max by Reinforcing Antioxidant and Osmotic Responses

Soybean is the most crucial oilseed and plant-protein crop worldwide, yet its yield is frequently threatened by salinity and drought stress. In this study, the chitinase gene AcCHI was cloned from the highly stress-tolerant plant Atriplex canescens and heterologously overexpressed in soybean to generate stable T3 homozygous transgenic lines. Wild-type and transgenic plants were subjected to water-withholding drought treatment, 20% PEG6000-induced osmotic stress, and 150 mM NaCl salt stress. After drought treatment, the survival rate of transgenic lines reached 2.66–2.69 times relative to wild-type plants. Under osmotic and salt stress conditions, AcCHI-overexpressing lines exhibited better-maintained photosynthetic performance, higher proline accumulation, and lower malondialdehyde (MDA) levels compared with wild-type controls. Enhanced antioxidant enzyme activities and weakened histochemical ROS staining were also observed in transgenic leaves. Stress-responsive genes associated with DREB, RD22, and SOS pathways showed stronger stress-inducible expression in transgenic plants. Our results show that heterologous AcCHI expression is associated with improved osmotic- and salt-stress tolerance in soybean seedlings under laboratory conditions. This study provides new observational insights into chitinase-linked abiotic-stress responses and offers candidate genetic resources for breeding stress-tolerant soybean varieties.