Dynamic changes of endogenous hormones and transcriptome analysis reveal the regulatory mechanism of gibberellin-promoted male cone formation in Platycladus orientalis

Platycladus orientalis is a unique monoecious coniferous tree species in China that plays an important role in urban landscaping and mountain afforestation. However, its large amount of pollen can easily trigger pollen allergy during spring. Clarifying the mechanisms underlying male cone formation and development in P. orientalis is essential for better controlling male cone production. Gibberellin (GA) is known to regulate various reproductive and developmental processes in plants. Although the regulatory role of GA in the reproductive transition of angiosperms has been relatively well characterized, its function in coniferous plants remains poorly understood. Therefore, this study elucidated gene expression mechanisms following GA treatment. The male cone quantity after GA application was statistically analyzed. The results showed that treatment with 150 mg/L GA3 produced the highest increase in male cone number, reaching 84.2%. Endogenous hormone contents and transcriptomic profiles of male cones at different stages after GA3 spraying were compared with those of the control group. During the reproductive transition and development, GA3 and IAA concentrations in the treatment group were markedly higher than in the control. While the contents of ABA and ZT were lower than those of the control group, and there was no significant difference in the differentiation stage. In total, 13,661 differentially expressed genes (DEGs) were identified across developmental stages. Among them, 201 DEGs were involved in endogenous hormone biosynthesis and signal transduction, and 85 DEGs were related to reproductive transition and development. These findings indicate that the reproductive transition in P. orientalis is regulated by interactions among multiple endogenous hormones. Furthermore, GO, KEGG, and WGCNA analyses were performed to construct a co-expression network associated with male cone initiation and development. Core regulatory genes, including GAI1, AGL8, GGM13, AP1, and AGL6, were identified and their expression patterns were revealed among different developmental stages. A gene regulatory network model describing GA-induced male cone formation and development in P. orientalis was established, revealing that the regulatory network from the vegetative to reproduction is more complex. This research provides a systematic and comprehensive understanding of the molecular mechanisms underlying male cone formation and development in P. orientalis.