Analysis of the transcriptome and related physiological indicators of tree peony ( Paeonia suffruticosa Andr.) plantlets before and after rooting in vitro

Difficulty in induction of adventitious rooting in vitro and poor survival of transplanted plantlets are the most important factors that restrict tissue culture of tree peony ( Paeonia suffruticosa ). The primary reason for the low transplant survival is that the plantlet ceases growth and is dormant after rooting. However, the mechanism for plantlet dormancy remains unclear. In this study, the transcriptome and contents of endogenous phytohormones, phenolic compounds, and carbohydrates in the leaves and stems of tree peony plantlets in vitro were analyzed before and during culture on rooting medium for 0, 15, 30, and 45 days. Significant differences in the contents of endogenous hormones, phenolic acids, and carbohydrates before and after rooting were observed. A total of 97.45 Gb clean data were obtained and 43,741 unigenes were assembled. The differentially expressed genes detected at the timepoints before and during culturing on rooting medium were predominantly enriched in the ‘plant hormone signal transduction’, ‘phenylpropanoid biosynthesis’, and ‘starch and sucrose metabolism’ pathways. The dormancy of the plantlet after culturing on rooting medium was directly correlated with the increase in abscisic acid (ABA) and decrease in gibberellic acid (GA 3 ) contents, which was regulated by auxin response factor ARF2, abscisic acid-receptor protein PYR/PYL, GA-signaling pathway DELLA protein SLR1, GA-receptor factor GID1 and PP2C proteins. Additionally, phenolic and carbohydrate metabolism were affected, thereby changing the phenolic compound and carbohydrate contents. This study provides a theoretical foundation for elucidating the dormancy and dormancy release mechanisms of tree peony plantlets in vitro.