The PsuAGL6 - PsuAP3L - PsuSUS3 model promotes double flower formation in tree peony
The flower type of tree peony is a crucial ornamental trait, determining both its ornamental and economic value. However, double-flower cultivars are relatively scarce, and the underlying regulatory mechanisms governing double flower formation remain unclear. Here, based on the transcriptome analysis of different floral organs from three flower types of ‘Zhaofen’, a total of 40 824 genes were identified, and the key genes PsuAP3L, PsuAGL6, and PsuSUS3 were screened out by integrating weighted gene co-expression network analysis (WGCNA), with high expression observed in the petals of double-petal flowers. Overexpression of PsuAP3L transformed the stamens into petal-like structures in Arabidopsis thaliana and significantly increased petal number in tree peony, while silencing it led to a reduction in petal number. Notably, both in vivo and in vitro experiments have demonstrated that PsuAGL6 could directly bind to the CArG-box element in the PsuAP3L promoter, positively regulating its transcription and thereby increasing the petal number. Furthermore, PsuAP3L can directly bind to the promoter of sucrose synthase PsuSUS3 and activate its expression through transcriptional activation. Transient overexpression and silencing experiments confirmed that both PsuAP3L and PsuAGL6 affect petal number by regulating PsuSUS3, thereby promoting double flower formation in tree peony. In addition, application of exogenous sucrose solution (1.5 g·L−1) effectively increases the number of petals in tree peony. This study demonstrates that the PsuAGL6-PsuAP3L-PsuSUS3 module regulates the double-flower trait in tree peony by promoting stamen petaloidy, thereby providing a theoretical foundation and practical strategies for breeding novel flower types.