The involvement of PsTCP genes in hormone-mediated process of bud dormancy release in tree peony (Paeonia suffruticosa).

Background: The complete dormancy release determines the quality of bud break, flowering and fruiting. While in tree peony (Paeonia suffruticosa Andr.), the insufficient accumulation of cold temperatures results in incomplete dormancy release and poor flowering quality.

Results: In order to investigate if phytohormone can replace the chilling requirement in south China and other similar regions, the roles of fluridone (Flu), gibberellin (GA₃), and their combination in the bud dormancy release process were analyzed. It demonstrated that the application of exogenous GA₃ and the mixture significantly expedited the dormancy release of tree peony at 23℃. Furthermore, the endogenous hormone levels provided evidence for the substantial impact of exogenous GA₃ on dormancy release, highlighting its potential involvement in the chilling-independent pathway of dormancy release. Transcriptome sequencing and analysis of expression profiles were conducted to identify the crucial genes implicated in the dormancy release mechanism of tree peony. Among numerous genes from diverse gene families, the particularly interesting were TEOSINTE BRANCHED 1, CYCLOIDEA, and PROLIFERATING CELL FACTORS-like genes (PsTCP3, PsTCP4, and PsTCP14), which had significant expression levels during the dormancy release process under different treatments. They were divided into two distinct sub-families based on their different domains. Specifically, PsTCP14 was classified under Class I, while PsTCP3 and PsTCP4 were classified under Class II. The analysis of expression patterns revealed a significant accumulation of the three PsTCPs in buds undergoing dormancy release, with clear upregulation observed in response to GA₃ and the mixture treatments. Additionally, the analysis of promoter activity demonstrated the sensitivity of PsTCP4 and PsTCP14 to GA₃ and Flu.

Conclusion: The application of exogenous GA₃ has been shown to effectively expedite the release of dormancy in tree peony through a pathway that is not dependent on chilling. Further research found that PsTCP genes might play a crucial role in this process. These findings contribute to the understanding of the molecular mechanism of PsTCPs in the hormone-mediated and temperature-independent release of bud dormancy in tree peony.