Populus wulianensis mainly grows in hilly and sloped areas and has strong resistance to adversity. Previous transcriptome studies have shown that a WRKY gene PwuWRKY48 is expression-induced under drought stress. In this study, we aim to characterize the gene’s structure and investigate its role in plant drought resistance. The results show that PwuWRKY48 (1113 bp) belongs to a class IIc WRKY subfamily and it was determined as a nuclear localization protein. The gene promoter region contains a variety of cis-elements in relation to stress resistance. Under drought stress, PwuWRKY48 was expression-induced in leaves and stems, 29.7 and 16.6 times those before treatment, respectively. Overexpressing PwuWRKY48 lines were associated with increased activities of peroxidase (POD) and superoxide dismutase (SOD), 2.5 and 1.6 times higher than those of the wild type. While malondialdehyde content (MDA), superoxide anion radical (O₂^·−), and relative conductivity were decreased by 20%, 30%, and 21.3%, proline and chlorophyll contents increased by 37.5% and 11.2%, respectively. This indicates that PwuWRKY48 efficiently improved the drought tolerance of transgenic plants. PwuWRKY48 can be used as a gene resource for molecular breeding of plant drought resistance.

Background: Catalpa bungei ‘Jinsi’ has excellent wood properties and golden texture, which is widely used in producing furniture and crafts. The lignin content and structural composition often determine the use and value of wood. Hence, investigating the characteristics of the annual dynamics of lignin anabolic metabolites in C. bungei ‘Jinsi’ and analyzing their synthesis pathways are particularly important. Methods: We carried out targeted metabolomics analysis of lignin synthesis metabolites using ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) on the xylem samples of C. bungei ‘Jinsi’ in February, April, July, October 2022, and January 2023. Results: A total of 10 lignin synthesis–related metabolites were detected: L-phenylalanine, cinnamic acid, p-coumaraldehyde, sinapic acid, p-coumaric acid, coniferaldehyde, ferulic acid, sinapaldehyde, caffeic acid, and sinapyl alcohol (annual total content from high to low). These metabolites were mainly annotated to the synthesis of secondary metabolites and phenylpropane biosynthesis. The annual total content of the 10 metabolites showed the tendency of “decreasing, then increasing, and then decreasing”. Conclusions: C. bungei ‘Jinsi’ is a typical G/S-lignin tree species, and the synthesis of G-lignin occurs earlier than that of S-lignin. The total metabolite content decreased rapidly, and the lignin anabolism process was active from April to July; the metabolites were accumulated, and the lignin anabolism process slowed down from July to October; the total metabolite content remained basically unchanged, and lignin synthesis slowed down or stagnated from October to January of the following year. This reveals the annual dynamic pattern of lignin biosynthesis, which contributes to improving the wood quality and yield of C. bungei ‘Jinsi’ and provides a theoretical basis for its targeted breeding.