Molecular Mechanism Of Floral Induction Difference Between C.perpetua And C.petelotii

Sect.Chrysanthae plants are of high ornamental value,with mostflowering once per year,but Camellia perpetua flowering multiple times per year.In order to investigate the flowering mechanism of C.perpetua and C.petelotii,we first analyzed the flower bud differentiation and flowering characteristics of C.perpetua and C.petelotii in different seasons.Through comparative transcriptome analysis,the gene expression differences of terminal bud and flower bud during peak and low flowering period were analyzed,and the function of Cper CEN1 gene was studied.The terminal buds of two kinds of c.camellia were treated with GA3 and other plant hormones to compare the effects of different hormones on dormancy,growth and development of terminal buds of two species of Sect.Chrysanthae.At the same time,FT genes and promoters were cloned of two species of Sect.Chrysanthae and transformed into Arabidopsis thaliana to analyze the functions,and to explore the relationship between FT and the difference of floral habit of two species of Sect.Chrysanthae.The results were obtained as follows:（1）It was found that most of the flower buds of two species of Sect.Chrysanthae were on the annual branches,and the flower buds of C.perpetua were mainly on the base of the terminal buds,which were differentiated from the axillary buds of the Scale base of the terminal buds.Flower buds were formed in annual branches of C.petelotii,Although there were axillary buds in the basal Scales of terminal buds,they could not be differentiated into flower buds.Anatomical observation,scanning electron microscopy and paraffin section of the terminal buds and flower buds of two kinds of Sect.Chrysanthae showed that there were no significant differences in the apical meristem of the terminal buds at different stages and the floral primordium and bract primordium of the flower buds at the initial stage of differentiation.These results suggested that the differences in floral habits of the two kinds of Sect.Chrysanthae might be caused by floral induction.（2）Comparative transcriptomic study was conducted on the peak（March）and low（September）stages of flower bud differentiation in C.perpetua.A total of 11 067 differentially expressed genes were screened,among which 628 genes were specifically expressed in flower buds,and151 genes were specifically up-regulated in flower buds.Through KEGG and GO enrichment analysis,37 differentially expressed genes were identified,mainly focusing on the pathways of starch and sucrose metabolism,plant hormone synthesis and signal transduction.The expression pattern analysis of PEBP family genes showed that Cper CEN1was significantly expressed in the terminal buds of march and September,while Cpet CEN1 was almost not expressed in the terminal buds.Further research found that the CEN1 genome sequence of the two kinds of Sect.Chrysanthae was complete,and there was no loss of function.The overexpression of Cper CEN1 delayed flowering and affected inflorescence development of Arabidopsis thaliana,suggesting that the difference in floral formation mechanism between the two kinds of Sect.Chrysanthae was not caused by CEN1,and there was a unique floral induction in C.perpetua.（3）GA₃,paclobutrazol,auxin,6-BA,zeaxin,trans-zeaxin and ethephon were used to treat the terminal buds of two kinds of Sect.Chrysanthae to analyze the effects of different hormones on terminal bud dormancy,growth and flower bud differentiation.The results show that the terminal buds of two kinds of Sect.Chrysantha were treated with GA₃（200mg/L）can form new shoots early,but no significant change in winter.In winter,two kinds of Sect.Chrysantha were palaced into the greenhouse for growth（the average temperature was about 10°C higher than the natural environment）,which induced the flower bud differentiation of C.perpetua.Under the same condition,PAC treatment could inhibit flower formation,and the determined results showed that the soluble sugar content was closely related to flower formation.（4）Cper FT and Cpet FT gene sequences contained 4 exons and 3introns;The similarity of nucleotide sequence of FT homologous gene was more than 91%,and there was only one amino acid difference in amino acid sequence,which was not a functional site.The 2.5 kb sequences upstream FT of two kinds of Sect.Chrysanthae were cloned with 98%similarity.In order to compare the expression characteristics and functional characteristics of FT of two kinds of Sect.Chrysantha,five expression vectors Cper FTpro::GUS and Cpet FTpro::GUS,35S::Cper FT,g Cper FT and g Cpet FT were constructed and were transformed into Col-0 and ft-10.The results showed that 35S::Cper FT can promote arabidopsis thaliana flowering very early,and can supplement ft-10.Cper FTpro::GUS and Cpet FTpro::GUS transformed into Col-0,which was expressed in leaf inflorescence flowers and silipes,but there was no significant difference in expression pattern.Further studies are needed to determine whether the Cper FT is different from Cpet FT,and is directly involved in multiple flowering of C.perpetua.