Discovery Of Genes Associated With Flowering Time In Tree Peonies Based On Transcriptome Comparison

Tree peony(Paeonia section Moutan) is one of the traditional flowers of China. It is the challenge for long-term that how to extend the flowering period in the developmemt of tree peonies. Most of the tree peonies flower once a year, however, some varieties can rebloom in the autumn. The reblooming character provides a potential approach to prolong the flowering period of tree peony. However, the molecular mechanism of reblooming in tree peony is unclear so far. In this study, a reblooming peony variety Paeonia×lemoinei’High Noon’were selected to study the reblooming process and a non-reblooming variety Paeonia×suffruticosa’Luo Yang Hong’as control. Using transcriptome sequencing, bioinformation, expression analysis and transgenic methods, the difference on gene extpression patterns associated with flowering time between’High Noon’and’Luo Yang Hong’was compared, which is helpful to analyze the causes to reblooming and discuss the gene function in regulation reblooming during floral formation. This study provides the foundation on understanding the molecular mechanism of reblooming.The main results were summarized as follows:1. By the study of the flowering habit and microscope observation during flower flower development, the difference of flower differentiation process was analyzed between in’High Noon’and ’Luo Yang Hong. The results showed two floral transitions in HN:one transition occurred in the growth buds in June and resulted in reblooming, and the other transition occurred within bud scales in August to introduce the next spring flowering.2. By using Solexa/Illumina RNA-Seq technologies, the transcriptome of the mix floral buds were sequencing in’High Noon’and’Luo Yang Hong’. The sequence of 4,627,059,840 nt and 4,874,739,300 nt were obtained and 63,962 and 59,275 unigene with an average length of 699 nt and 698 nt were yielded by de novo assembly.3. The 16,764 differentially expression genes were obtained by using quantidication RNA-Seq technology in the buds during the floral induction in’High Noon’and’Luo Yang Hong’. The eight differentially expression genes related to flowering time determination were choosed, which are PsGA20OX, PsGID 1, PsCO, PsGO, PsFRI, PsVIN3, PsSOCl and PsFT.4. By using qRT-PCR technolology, the expression pattern of the differentially expressed genes was analyzed in two varieties around the year. Combined with biological observation and morphological identification, the four genes of PsFT, PsVIN3, PsCO and PsGA20OX were found that may be closely related with autumn reblooming in’High Noon’, which has presented high concentration and similarity pattern during reblooming.5. Transgenic experiments were carried in the two candidate genes of PsFT and PsSOCl. The result showed that over-expression the PsFT gene in Arabidopsis thaliana significantly induced early flowering and the flowering time is early with 14 days than wild-type Arabidopsis thaliana. Over-expressed the PsSOC1 gene had no significant effect in flowering time in A. thaliana.In summary, our study showed that reblooming in’High Noon’is determined by twice floral inductions, and the up-regulation of expression of PsVIN3, PsCO and PsGA20OX combined the peak expression of PsFT during induction and differentiation, thus induced the autumn reblooming. In this study, the high quality and comprehensive transcriptome database were constructed and the key candidate genes involved in reblooming were screened. This research provided genes resources for the gene engineering to improve flowering time, which have important theoretical significances and practical values.