Transcriptome Analysis of Active Axillary Buds from Narrow-crown and Broad-crown Poplars Provides Insight into the Phytohormone Regulatory Network for Branching Angle

The branching angle is an important trait for controlling the crown architecture of trees. It is not only under genetic regulation, but is also affected by other factors such as environmental and hormones. It is of great significance to explore the molecular regulation mechanism of poplar branching angle; In this paper, transcriptome sequencing technology was used to generate cDNA libraries from axillary buds of the cultivar ‘Zhonglin 2025’ (a broad-crown poplar; BC) and Populus × zhaiguanheibaiyang (a narrow-crown poplar; NC). NC is characterized by a smaller branch angle than BC, a narrow crown shape, and rapid growth. At the same time, the transcriptome results were verified by qRT-PCR; The results showed that 193.4 million high-quality pure readings were obtained from the BC and NC cDNA libraries, and 1609 DEGs were detected, of which 822 were upregulated and 787 were downregulated. On the basis of functional annotation of the DEGs with gene ontology terms, 41 genes were associated with hormone synthesis and metabolism, 85 genes were associated with auxin transport, and 101 genes were involved in hormone signal transduction. The expression patterns of 12 DEGs associated with branch angle development were verified by qRTPCR, which revealed that the expression patterns were consistent with the results of transcriptome analysis. Quantification of phytohormone contents in axillary buds of NC and BC revealed that auxin content showed the greatest significant difference between NC and BC; Finally, we constructed a model for the phytohormone regulatory network associated with branching angle. It hopes to provide reference for the study of the molecular mechanism of poplar branching angle.