Physiological and Molecular Adaptation of the Ahuehuete (Taxodium mucronatum Ten.) to Waterlogging

Ahuehuete (Taxodium mucronatum Ten.) is a riparian tree species of significant ecological, cultural, and economic importance, demonstrating remarkable tolerance to prolonged flooding. However, the underlying mechanism of waterlogging adaptation remains unknown. In this study, we determined the physiological traits of the Ahuehuete leaves at 0, 15, 30, and 60 d under waterlogging conditions. The results showed that no significant difference in MDA content occurred between the Ahuehuete leaves subjected to waterlogging and those under well-watered (CK) conditions. In contrast, the contents of osmoprotectants (soluble sugar, soluble protein, and proline) and the activities of antioxidant enzymes (SOD, POD, and CAT) exhibited similar change trends under both waterlogging and CK conditions, despite minor quantitative differences between the two groups. Subsequent comparative transcriptome analysis was performed to investigate the transcriptional characteristics. A total of 3687 DEGs were expressed in all comparisons throughout the waterlogging process, while 2873, 4617, and 2710 DEGs were comparison group specific. KEGG enrichment analysis revealed that DEGs were enriched in various metabolic pathways, such as Plant hormone signal transduction (ko04075), MAPK signaling pathway-plant (ko04016), ABC transporter (ko02010), and Nitrogen metabolism (ko00910). WGCNA also identified key modules associated with physiological traits, simultaneously emphasizing the importance of plant hormone signal transduction and MAPK signal cascade. Overall, our findings revealed physiological and transcriptomic characteristics of the Ahuehuete under waterlogging conditions, and provided new insights to waterlogging adaptation in woody gymnosperm species.