Transcriptome sequencing of active buds from Populus deltoides CL. and Populus × zhaiguanheibaiyang reveals phytohormones involved in branching.

Branching in woody plants affects their ecological benefits and impacts wood formation. To obtain genome-wide insights into the transcriptome changes and regulatory mechanisms associated with branching, we performed high-throughput RNA sequencing to characterize cDNA libraries generated from active buds of Populus deltoides CL. 'zhonglin2025' (BC) and Populus × zhaiguanheibaiyang (NC). NC has more branches than BC and rapid growth. We obtained a total of 198.2 million high-quality clean reads from the NC and BC libraries. We detected 3543 differentially expressed genes (DEGs) between the NC and BC libraries; 1418 were down-regulated and 2125 were up-regulated. Gene ontology functional classification of the DEGs indicated that they included 89 genes that encoded proteins related to hormone biosynthesis, 364 genes related to hormone signaling transduction, and 104 related to the auxin efflux transmembrane transporter. We validated the expression profiles of 16° by real-time quantitative PCR and found that their expression patterns were similar to those obtained from the high-throughput RNA sequencing data. We also measured the hormone content in young buds of BC and NC by high-pressure liquid chromatography. In this study, we identified global hormone regulatory patterns and differences in gene expression between NC and BC, and constructed a hormone regulatory network to explain branching in Populus buds. In addition, candidate genes that may be useful for molecular breeding of particular plant types were identified. Our results will provide a starting point for future investigations into the molecular mechanisms of branching in Populus.