Genome-Wide Identification of the XTH Gene Family in Carya illinoinensis and Heterologous Expression Analysis of CiXTH18 Under Osmotic Stress

Drought stress severely restricts the growth and yield of woody nut crops. The xyloglucan endotransglucosylase/hydrolase (XTH) gene family participates in plant developmental and stress responses, yet its functions in pecan (Carya illinoinensis) under water limitation remain largely uncharacterized. Here, we performed a genome-wide identification of the XTH family in pecan, identifying 34 members distributed across four phylogenetic clades. Transcriptome-based expression analysis showed that several CiXTH genes responded to drought stress, among which CiXTH18 exhibited strong and sustained induction. To investigate its function, CiXTH18 was overexpressed in Arabidopsis thaliana. Under PEG-induced osmotic stress, CiXTH18-overexpressing lines exhibited significantly prolonged primary root lengths compared to wild-type plants. Furthermore, detached leaf assays revealed that transgenic plants had lower water loss rates under dehydration conditions. In addition, DAB staining indicated reduced H2O2 accumulation in CiXTH18-overexpressing plants under osmotic stress. Quantitative real-time PCR analysis revealed that the drought-responsive gene DREB2A and the ABA biosynthesis-related gene NCED3 were more strongly induced in transgenic lines than in wild-type plants after PEG treatment. Promoter activity assays confirmed that CiXTH18 was responsive to ABA treatment. Collectively, our findings indicate that heterologous expression of CiXTH18 is associated with improved performance of Arabidopsis under PEG-induced osmotic stress and support CiXTH18 as a promising candidate for further functional investigation.