Exogenous Salicylic Acid Alleviates Waterlogging Stress in Xanthoceras sorbifolium: Physiological Mechanisms and Molecular Regulation

A major Chinese woody oil plant with unsaturated-fatty-acid-rich seeds for biodiesel and edible oil, Xanthoceras sorbifolium tolerates drought but not waterlogging; salicylic acid (SA), a key stress response signal, is inexpensive, safe, and effective for enhancing stress tolerance. Two-year-old saplings of Xanthoceras sorbifolium were used as materials. They were sprayed with 0.5 mmol·L−1 SA for 3 days (based on prior studies), and then waterlogged for 10 days; physiological and transcriptomic data were collected. SA significantly increased height, diameter, and root dry weight by 392.6%, 450.0%, and 242.4% compared to water control; enhanced osmotic regulatory substances, antioxidant enzyme activities, secondary metabolites, and root activity; and reduced malondialdehyde content and relative electrical conductivity by 23.40% and 148.7%. SA-enhanced antioxidant defense correlated with synergistic transcriptional regulation. Transcriptome analysis showed that SA up-regulated key enzyme genes involved in flavonoid synthesis, such as PAL and 4CL, and regulated hormone signal transduction-related genes such as SAUR and DELLA. Key transcription factor genes were also screened, mainly including members of the MYB, bHLH, and ERF families. SA alleviated waterlogging damage. Meanwhile, this study provides valuable insights into the molecular basis of the response to waterlogging stress regulated by salicylic acid, and offers important theoretical and practical significance for the promotion and cultivation of Xanthoceras sorbifolium in rainy southern regions of China.