Sophora japonica L. is an important landscaping and ornamental tree species throughout southern and northern parts of China. The most common color of S. japonica petals is yellow and white. In this study, S. japonica flower color mutants with yellow and white flag petals and light purple-red wing and keel petals were used for transcriptomics and metabolomics analyses. To investigate the underlying mechanisms of flower color variation in S. japonica ‘AM’ mutant, 36 anthocyanin metabolites were screened in the anthocyanin-targeting metabolome. The results demonstrated that cyanidins such as cyanidin-3-O-glucoside and cyanidin-3-O-rutinoside in the ‘AM’ mutant were the key metabolites responsible for the red color of the wing and keel petals. Transcriptome sequencing and differentially expressed gene (DEG) analysis identified the key structural genes and transcription factors related to anthocyanin biosynthesis. Among these, F3′5′H, ANS, UFGT79B1, bHLH, and WRKY expression was significantly correlated with the cyanidin-type anthocyanins (key regulatory factors affecting anthocyanin biosynthesis) in the flag, wing, and keel petals in S. japonica at various flower development stages.

Transgenic technology is a potent tool for verifying gene functions, and poplar serves as a model system for genetically transforming perennial woody plants. However, the current poplar genetic transformation system is limited to a few genotypes. In this study, we developed an efficient transformation system based on the Agrobacterium-mediated transformation of Populus wulianensis, a rare and endangered tree species endemic to Shandong Province. Aseptic seedlings of P. wulianensis were used as experimental materials, and the optimal medium for inducing adventitious buds was explored as 1/2(NH₄NO₃) MS + 0.05 mg/L naphthalene acetic acid (NAA) + 0.5 mg/L 6-benzylaminopurine (6-BA), resulting in up to 35 adventitious buds. The selection resistance critical pressure of 300 mg/L for timentin can effectively inhibit the growth of Agrobacterium while promoting the induction of adventitious buds in leaves. The critical screening pressure for kanamycin for producing resistant adventitious buds and inducing resistant rooting seedlings was 100 mg/L. We optimized several independent factors, which significantly enhanced the efficiency of genetic transformation. The leaves were infected with Agrobacterium suspension diluted twice by adding 100 μmol/L acetylsyringone (β-AS) (OD₆₀₀ = 0.6) for 15 min, followed by co-culture in the dark for 3 d. Using this improved transformation system, we obtained transgenic P. wulianensis clones overexpressing the enhanced green fluorescent protein (EGFP) gene through direct organogenesis. Among the 112 resistant buds obtained, 17 developed resistant rooting in seedlings. Eight positive plants were identified through DNA, RNA, and protein level analyses, with a positivity rate of 47.06%. This study provides a foundation for developing and utilizing P. wulianensis germplasm resources and lays the groundwork for resource improvement.

Flower color serves as a vital ornamental feature of landscape plants; Sophora japonica L. mutant ‘AM’ exhibits the different colors from the common S. japonica. ‘AM’, presenting with a light purple-red wing and keel and yellowish-white flag petals, while common S. japonica is yellow and white. The metabolites contributing to this color specificity in red-flowered S. japonica ‘AM’ are not yet fully understood. In this study, the flag, wing, and keel petals were collected from ‘AM’ at various phases, including the flower bud phase, initial flowering phase, full bloom phase, and final flowering phase, for conducting the metabolic assays targeting anthocyanins. Subsequently, we identified 45 anthocyanin-related metabolites, including nine flavonoids and 36 anthocyanins. Ten major floral chromoside metabolites were found to affect the coloration differences among the petals, where the most abundant anthocyanin was cyanidin-3-O-glucoside (Cy3G), which was much higher in the keel petal (LGB) and wing petal (YB) than in the flag petal (QB), and similarly, during the four periods of different petal types, the Cy3G content was higher in the initial flowering stage (S2), the full bloom stage (S3), and the final flowering stage (S4) than the flower bud stage (S1), which was in accordance with the trend of the observed petal floral color phenotypic difference measurement correlation. This suggested that the Cy3G accumulation was the primary factor driving the distinct coloration of varying types of petals. These findings could contribute to the understanding of the biochemical mechanisms underlying S. japonica petal coloration and may support future efforts in flower color improvement.