Transcriptomic Analysis Reveals Hormonal Control of Shoot Branching in Salix matsudana

Shoot branching is regulated by axillary bud activities, which subsequently grow into branches. Phytohormones play a central role in shoot branching control, particularly with regard to auxin, cytokinins (CKs), strigolactones (SLs), and gibberellins (GAs). To further study the molecular basis for the shoot branching in Salix matsudana, how shoot branching responds to hormones and regulatory pathways was investigated, and potential genes involved in the regulation of shoot branching were identified. However, how these positive and inhibitory processes work on the molecular level remains unknown. RNA-Seq transcriptome expression analysis was used to elucidate the mechanisms underlying shoot branching. In total, 102 genes related to auxin, CKs, SLs, and GAs were differentially expressed in willow development. A majority of the potential genes associated with branching were differentially expressed at the time of shoot branching in S. matsudana, which have more number of branching. These findings are consistent with the growth and physiological results. A regulatory network model was proposed to explain the interaction between the four hormones that control shoot branching. Collectively, the results presented here contribute to a more comprehensive understanding of the hormonal effects on shoot branching in S. matsudana. In the future, these findings will help uncover the interactions among auxin, SLs, CKs, and GAs that control shoot branching in willow, which could help improve plant structures through the implementation of molecular techniques in targeted breeding.