Genome-Wide Identification and Characterization of the Xyloglucan Endotransglucosylase/Hydrolase (XTH) Gene Family in Camellia oleifera and the Function of CoXTH1 During Drought Stress

Xyloglucan endotransglucosylase/hydrolase (XTH) plays a significant role in plant responses and adaptation to abiotic stresses. However, the <i>XTH</i> gene family in <i>Camellia oleifera</i> remains largely unknown. Herein, 31 <i>CoXTH</i> genes from the <i>C. oleifera</i> genome, which were clustered into four evolutionary groups, were identified. Notably, <i>CoXTH1</i>, <i>CoXTH6</i>, <i>CoXTH14</i>, <i>CoXTH28</i>, and <i>CoXTH31</i> showed significant upregulation under drought stress, suggesting their importance in stress responses. Furthermore, heterologous expression of <i>CoXTH1</i>, <i>CoXTH14</i>, and <i>CoXTH28</i> in yeast improved yeast survival under drought stress. Overexpressing <i>CoXTH1</i> in <i>Arabidopsis thaliana</i> significantly enhanced drought tolerance, characterized by improved seedling growth, increased antioxidant enzyme activity, and reduced reactive oxygen species (ROS) levels. Notably, transgenic expression of <i>CoXTH1</i> significantly elevated the contents of xyloglucan, leading to increased cellulose, and hemicellulose contents in the plants. The elevated hemicellulose and cellulose strengthen the cell wall structure, maintaining cellular integrity and stability, and improving plant drought tolerance. These findings lay a foundation for understanding the functional roles of <i>CoXTH</i> genes and highlight <i>CoXTH1</i> as a potential candidate gene for improving drought tolerance in <i>C. oleifera</i> and other woody crops.