Effects Of PdSPLs On The Juvenile-to-Adult Phase Transition In Paeonia Delavayi Franch

Tree peony(Paeonia suffruticosa) originated in China, with long cultivation history and profound cultural background. But the cross breeding is limited by long juvenile stage. This work explored the mechanism of juvenile-to-adult phase transition in terms of the morphological, physiological and molecular aspects in Paeonia delavayi to provide theoretical basis for the tree peony cross breeding. The main results were as follows:1. The morphological indexes(plant height, crown width, leaf area, leaf length and width, petiole length) and physiological indexes(contents of chlorophyll, soluble sugar, starch and soluble protein) of different age plants were studied and analyzed. The results revealed that plant height and crown width increased with the growth of the plant; leaf area, leaf length, leaf area, soluble sugar content and starch content in 1-year-old plants were significantly lower than 2- and 3-year-old plants. The contents of chlorophyll and soluble protein decreased with the growth of the plant. The microscopic observation of flower bud differentiation showed that 1-year-old plants remained vegetative growth, while 2-year-old and 3-year-old plants remained reproductive growth. The plant height and leaf area could be acted as the main morphological indexes in juvenile-to-adult transition. It was speculated that the transition was in the second year growth.2. Three members of SPL(SQUAMOSA promoter binding protein-like) gene family(Pd SPL9, Pd SPL12 and Pd SPL13) were cloned. The open reading frame(ORF) were 1125 bp, 1404 bp and 1086 bp respectively, encoding 374, 467 and 361 amino acid(AA) residues. Alignments of the AA sequences revealed that Pd SPL9, Pd SPL12 and Pd SPL13 shared height identity with SPL proteins from other plants and contain a conserved domain, which possessed the characteristics of the SPL family. The results also showed that there is a Pdmi R156 a binding site in Pd SPL9 and Pd SPL13 except for Pd SPL12. Pd SPL9 and Pd SPL13 were regulated by Pdmi R156 a.3. The q RT-PCR analysis of Pd SPL9, Pd SPL12 and Pd SPL13 in different organs and buds of different age plants and in different nodes showed that: the highest expression levels of Pd SPL9 were appeared in buds, followed by seeds and roots. The expression of Pd SPL9 increased with the growth of the plant. The expression of Pd SPL9 in the first lateral buds was significantly higher than the second and third lateral buds. Pd SPL12 expressed in all organs and increased with the growth of the plant. Pd SPL13 expressed only in buds. There was no significant difference in different year plants and different nodes. As the upstream gene of Pd SPL9, Pdmi R156 a decreased with plants growth, While Pdmi R172 d and Pd LFY, the downstream genes of Pd SPL9, had an opposite expression pattern. The expression of Pd SOC1 had nothing to do with Pd SPL9. These results made us to speculate that Pd SPL9 may regulate the juvenile-to-adult phase transition by regulating the expression of Pd LFY in Paeonia delavayi.4. The transgenic experiment showed that overexpression of Pd SPL9 reduced the number of rosette leaves and promoted the juvenile-to-adult phase transition, bolting and flowering. The q RT-PCR showed that Pd SPL9 promoted the expression of At SOC1 and At LFY in transgenic lines. These results confirmed that Pd SPL9 may control the juvenile-to-adult phase transition by regulating the expression of Pd LFY in P. delavayi.