Genetic Responses to Drought and Waterlogging Stresses of Longleaf Speedwell (<em>Pseudolysimachion longifolium</em>)

Climate change necessitates a deeper understanding of plant tolerance mechanisms to dual water stresses. This study investigated the distinct physiological and genetic responses of Longleaf Speedwell (Pseudolysimachion longifolium) to drought and waterlogging using RNA-Seq. Physiological data showed a rapid and comparable reduction in photosynthetic efficiency after one week and biomass under both stresses after two weeks. However, transcriptomic analysis revealed fundamentally distinct strategies: Drought induced a massive transcriptional upheaval (5 times more DEGs), characterized by the upregulation of defense pathways (e.g., Phenylpropanoid biosynthesis) and the severe shutdown of growth-related metabolism (e.g., Ribosome, Photosynthesis). In contrast, waterlogging triggered a constrained hypoxic response, prioritizing energy conservation by downregulating synthesis processes (Nitrogen, Arginine biosynthesis) and activating ethylene signaling. The reliability of the RNA-Seq data was confirmed by qRT-PCR, which also crucially identified Alcohol dehydrogenase (ADH), Ethylene Responsive Factor (ERF), and Peroxidase (POD) as common candidate genes highly induced under both drought and waterlogging conditions, suggesting a generalized role in broad-spectrum water stress tolerance. These findings provide critical molecular evidence demonstrating the divergent and specific adaptive strategies of P. longifolium to different water regimes and highlight ADH, ERF, and POD as promising targets for engineering broad-spectrum water stress tolerance.