Elucidation of the mechanism of reflowering in tree peony (Paeonia suffruticosa) 'Zi Luo Lan' by defoliation and gibberellic acid application.

In this study, the reflowering mechanism of tree peony (Paeonia suffruticosa 'Zi Luo Lan') after defoliation and gibberellic acid (GA) application (autumn-flowering treatment) was investigated by monitoring the morphological changes, measuring the endogenous GA3 and abscisic acid (ABA) contents, and determining the expression patterns of six GA- and two ABA-related genes. The results show that autumn-flowering treatment induced tree peony reflowering in autumn, which was accompanied by nutrient absorption in buds. The application of exogenous GA3 induced a simultaneous increase in GA3 and decrease in ABA levels, suggesting that the high ratios of GA3/ABA may play a key role in inducing tree peony reflowering. RT-qPCR analysis shows that PsCPS and PsGA2ox were significantly induced and inhibited by GA3 application, respectively, which supports the hypothesis that GA3 treatment induces endogenous GA3 production. In addition, GA3 treatment inhibited the expression of the PsGID1c, but its effect on PsGAI1 was limited, whereas the expression of PsGAMYB could be GA- or ABA-related. Furthermore, autumn-flowering treatment significantly inhibited the expression of PsNCED and PsbZIP, which coincides with the observed changes in ABA levels. Therefore, we postulate that autumn-flowering treatment induces tree peony reflowering by inhibiting the function of ABA accumulation and signaling.