Identification and Expression Profiles of Xyloglucan Endotransglycosylase/Hydrolase Family in Response to Drought Stress in Larix kaempferi

Xyloglucan endotransglucosylase/hydrolase (XTH) is a crucial enzyme in plant cell wall remodeling, which contributes to plant growth, development, and stress response. Based on the transcriptome data of <i>Larix kaempferi</i>, this study identified and analyzed 16 <i>XTH</i> genes. Sequence alignment and phylogenetic analysis indicated that the <i>LkXTH</i> gene family can be divided into three subfamilies, namely the Early Diverging Group, Group I/II, and Group III, all of which share highly conserved motifs and structural features. Expression profiling demonstrated that <i>LkXTH</i> genes are actively expressed in the roots, stems, and leaves of <i>L. kaempferi</i>. Under drought stress, the expression of <i>LkXTH1</i>, <i>LkXTH2</i>, <i>LkXTH3</i>, <i>LkXTH4</i>, <i>LkXTH6</i>, <i>LkXTH14</i>, <i>LkXTH15</i>, <i>LkXTH17</i>, and <i>LkXTH18</i> increased rapidly in roots. Meanwhile, the expression levels of <i>LkXTH5</i>, <i>LkXTH7</i>, <i>LkXTH8</i>, and <i>LkXTH13</i> exhibited significant upregulation in leaves. Notably, <i>LkXTH11</i> and <i>LkXTH16</i> significantly increased in both roots and leaves, with a more pronounced increase in leaves, but <i>LkXTH10</i> displayed significant upregulation in the stems. Furthermore, the heterologous expression of <i>LkXTH1</i> and <i>LkXTH17</i> in yeast significantly enhances drought tolerance. These findings indicate that individual <i>LkXTH</i> genes exhibit distinct organ-specific responses to drought stress, thereby advancing our understanding of their functional roles in larch drought response.