Morphological and physiological changes, and the functional analysis of PdSPL9 in the juvenile-to-adult phase transition of paeonia delavayi

Abstract

Tree peony has a long juvenile stage, which has limited breeding efforts. To date, very little information is available regarding the juvenile stage of tree peony. In the present study, Paeonia delavayi plants of varying ages were used to investigate the juvenile phase, juvenile-to-adult phase transition, and adult phase via morphological, physiological, and molecular genetic analysis. Micro-observation of buds of different ages and flower induction experiments suggested that the juvenile-to-adult phase transition of P. delavayi occurred at around 2-years of age. Plant height, crown width, leaf length, and the soluble sugar and starch content were positively correlated with plant age. The juvenile gene PdSPL9 contained miR156 targeted sites and a typical SBP domain was cloned from P. delavayi. Expression analysis showed that the expression levels of PdSPL9, PdmiR172d, and PdLFY increased with plant age, while the inverse pattern was observed for PdmiR156a. Function of PdSPL9 was further characterized in Arabidopsis plant. According to function characterization of PdSPL9 in Arabidopsis and expression patterns of PdSPL9 in P. delavayi, it was suggested that PdSPL9 plays a role in controlling juvenile-to-adult phase transition by promoting miR172d, and PdLFY expression in P. delavayi plants, while the expression of PdSPL9 is repressed by miR156a.