Branching in long-lived plants can cause scarring at the base and affect wood density, which greatly inhibits wood yield and quality. Eucalyptus urophylla is one of the most important commercial forest tree species in South China, with diverse branch number and branch angles under different genetic backgrounds. However, the main elements and regulatory mechanisms associated with different branching traits in E. urophylla remain unclear. To identify the factors that may influence branching, the transcriptome and metabolome were performed on the shoot apex (SA), lateral shoot apex (LSA), and stem segment at the 5th axillary bud from the shoot apex (S1) in lines ZQUC14 (A) and LDUD26 (B), with A exhibiting a smaller Ba than B. A total of 307.3 million high-quality clean reads and nine hormones were identified from six libraries. Several differentially expressed regulatory factors were identified between the two genotypes of E. urophylla. The Kyoto Encyclopedia of Genes and Genomes pathways were enriched in plant hormone signal transduction, plant hormone biosynthesis and their transport pathways. Furthermore, gene expression pattern analysis identified genes that were significantly downregulated or upregulated in S1 relative to the SA and LSA segments, and the plant hormone signal transduction pathway was constructed to explain branching development. This study clarified the main plant hormones and genes underlying branch numbers and angles of E. urophylla, confirmed that ABA and SA could promote a larger branch angle and smaller branch number, while IAA has an opposite function. Numbers of key candidate genes involved in plant hormone signal transduction were found in the positive regulation of branch formation. These novel findings should aid molecular breeding of branching in Eucalyptus.

长生植物分枝会在基部产生疤痕，影响木材密度，极大地抑制木材产量和质量。尾叶桉是华南地区最重要的商品林树种之一，在不同的遗传背景下具有不同的分枝数和分枝角度。然而，尾叶石斛不同分枝性状的主要成分和调控机制仍然不清楚。为了确定可能影响分枝的因素，在株系 ZQUC14 (A ) 和 LDUD26 (B)，其中 A 的 Ba 比 B 小。从六个文库中总共鉴定出 3.073 亿个高质量的干净读数和九种激素。在E. urophylla的两种基因型之间确定了几种差异表达的调节因子。京都基因和基因组途径百科全书富含植物激素信号转导、植物激素生物合成及其转运途径。此外，基因表达模式分析确定了相对于 SA 和 LSA 片段在 S1 中显着下调或上调的基因，并构建了植物激素信号转导途径来解释分枝发育。本研究阐明了尾叶石斛分枝数和角度的主要植物激素和基因，证实ABA和SA可以促进更大的分支角度和更小的分支数量，而IAA具有相反的功能。在分支形成的正调控中发现了参与植物激素信号转导的关键候选基因的数量。这些新发现应该有助于桉树分枝的分子育种。