Exogenous gibberellin promotes lateral branch development in stumping Pinus yunnanensis by regulating endogenous hormones and TCP genes

While plant stumping can break apical dominance, promote lateral branching, and thereby increase yield, a significant technical challenge remains in further enhancing the coppicing regrowth capacity after stumping. This study used one-year-old Pinus yunnanensis Franch seedlings as subjects. Through exogenous application of gibberellin 3 (GA 3 ) and Paclobutrazol (PAC), it investigated the regulatory role of gibberellin (GA) in sprouting and identified TCP genes related to branching within the GA pathway. Results indicate that exogenous hormone treatments altered endogenous hormone levels in P. yunnanensis seedlings. Exogenous GA 3 treatment significantly increased endogenous IPA, ABA, GA 3 , GA 1 , SA, and SAG content. Correlation analysis with sprout number revealed a positive relationship between endogenous hormones and sprout number, indicating that exogenous GA 3 significantly influenced sprout number. After hormone application, the cumulative number of sprouts increased with seedling age across all treatments. Therefore, to further investigate whether changes in sprout number were caused by gene alterations in the GA signaling pathway, this study analyzed the GA signaling pathway and its associated transcription factors. Fifteen TCP family members were screened from the P. yunnanensis transcriptome, phylogenetically classified into Class I and Class II subfamilies. Conserved motif sites within the Class II family co-occurred, exhibiting high conservation. Genes from the Class II subfamily were cloned, and their differential expression across various tissues was analyzed via real-time quantitative PCR. Expression patterns under different hormone treatments were also examined. Our results reveal that PyTCP4, PyTCP6 , and PyTCP20 are significantly upregulated by PAC (a GA synthesis inhibitor) and show strong negative correlations with sprouts number, while GA 3 treatment partially alleviates this effect. These findings provide direct evidence that TCP transcription factors act as repressors of shoot branching, linking their hormone-responsive expression to the regulation of sprouts formation in P. yunnanensis . These results indicate that TCP transcription factors play a crucial role in shoot and root emergence, with their expression influenced by exogenous hormones, thereby affecting the growth and development of emerging shoots and roots. This provides a reference and basis for analyzing the expression patterns and functions of TCP genes in P. yunnanensis , facilitating further research into their functions.