Transcriptome of Two-Hybrid Poplar ( × ) During Adventitious Root Formation After Stem Cutting.

Poplar ( spp.) is an economically and ecologically important temperate tree species known for its rapid growth. Clonal propagation has facilitated genetic advancements, but it remains challenging due to substantial variations in rooting capacity among poplar species and clones. Poplar clones were divided into two groups based on their rooting ability (high or low), and their transcriptome was analyzed for 3 weeks following stem-cutting propagation to investigate the rooting mechanisms of a hybrid of two fast-growing poplar species ( × ). The root length and area of the high-rooting group were 668.7% and 198.4% greater than those of the low-rooting ability group, respectively (maximum < 0.001). Compared to week 0, genes involved in auxin signaling, cell wall organization, and secondary metabolite biosynthesis were consistently upregulated at 1, 2, and 3 weeks after planting, respectively. The expression of genes associated with cell wall differentiation and flavonoid biosynthesis was greater in the high- than in the low-rooting group at week 2. and transcription factors, which regulate flavonoid biosynthesis, as well as chalcone isomerase, a key enzyme in early flavonoid biosynthesis and root formation, were upregulated in the high-rooting group. The flavonoid biosynthesis pathway is important in rooting after stem cutting of × hybrids.