Physiology and transcriptomic analysis of endogenous hormones regulating in vitro adventitious root formation in tree peony

The difficulty of rooting is the bottleneck of micropropagation in tree peony. Endogenous hormone is the key factor to regulate adventitious roots formation, but the research on the exploration of its related mechanisms is still lagging. In this study, the changes in endogenous hormone content during adventitious root formation were investigated in Paeonia × lemoinei ‘High Noon’. Transcriptome sequencing was carried out at five key time points of rooting. The results showed that the in vitro adventitious roots of tree peony formed from induced root primordium, which mainly originated from vascular bundles. However, a few roots originated from the callus. The progress of adventitious root formation can be divided into three stages. IAA (3-Indoleacetic Acid), ZR (trans-Zeatin-riboside), and GAs (Gibberellins) were positively correlated with adventitious root primordia. The trend of ABA (Abscisic Acid) and IAA was opposite, and ABA is related to the stress resistance of in vitro shoots. Plant hormone signal transduction was identified as a key metabolic pathway regulating adventitious root formation. Twenty-eight key genes were mined in this pathway. Using weighted gene co-expression network analysis, 17 hub genes were identified in the co-expression network of hormone trait-related modules. Through a comprehensive analysis, a hypothesis model of endogenous hormones regulating adventitious root formation in tree peony was preliminarily constructed. The results of this study can provide rich genetic resources and a direction for further exploring the molecular mechanism of adventitious root formation in tree peony.