Sugar Content And Transcriptome Analysis During Two Flower Bud Differentiation Of Magnolia Liliflora ‘Hongyuanbao’

Magnolia is a common ornamental plant in spring.Most Magnolia plants only bloom once a year,but a few Magnolia plants always bloom in spring and summer.At present,the study on the nutritional effects and related molecular mechanisms of multiple flowering of Magnolia is still unclear.In this study,the contents of endogenous sucrose and trehalose in the flower buds,stems and leaves of Magnolia liliflora ‘Hongyuanbao’were determined during the pre-middle-post periods of two flower bud differentiation stages.Subsequently,combined transcriptome and metabolome analysis was performed on flower buds at six stages.Finally,the expression of trehalose-phosphate synthase gene of ‘Hongyuanbao’was detected by q RT-PCR,and the key Ml TPS1 gene was selected and cloned by PCR..The main results are as follows:(1)Analysis of sucrose and trehalose change during the two flower bud differentiation stages of ‘Hongyuanbao’:the content of sucrose and trehalose in leaves and buds were always higher than that in stems during the two flower bud differentiation stages of ‘Hongyuanbao’.The change trends of sucrose and trehalose in different tissues during the first and second flower bud differentiation were not consistent.The content of trehalose and sucrose in buds increased significantly at the first,middle and last periods of the second differentiation compared with the corresponding periods of the first differentiation stage.(2)Flower bud transcriptome analysis during the two flower bud differentiation stages of ‘Hongyuanbao’:a total of 43 257 genes were obtained by transcriptome sequencing,of which 28 397 genes could be annotated.Comparison of different genes in two flower bud differentiation showed that S2 vs S5,namely the middle stage of the second flower bud differentiation and the middle stage of the first flower bud differentiation,had the largest number of different genes,with a total of 4074 genes,and these different genes were mainly involved in phenylpropane biosynthesis and carbon metabolism.A total of 35 flower-forming genes were screened bytranscriptome,among which 14 genes were involved in photoperiod pathway.(3)Differentiation metabolic pathways screening of ‘Hongyuanbao’:Combined transcriptome and metabolome analysis,we found strongly correlated differential genes and metabolites in 8 key metabolic pathways.They were ko01200 Carbon metabolism,ko00630 Glyoxylate and dicarboxylate metabolism,ko02010 ABC transporters,ko00052 Galactose metabolism,ko00460 Cyanoamino acid metabolism,ko00280 Valine,leucine and isoleucine degradation,ko00240 Pyrimidine metabolism and ko00500 Starch and Sucrose metabolism pathway.In sucrose and starch metabolic pathway,differential metabolites sucrose,trehalose 6 phosphate and trehalose were significantly increased.(4)Expression and sequence analysis of TPS genes in the two flower bud differentiation of ‘hongyuanbao’:Ml TPS1 expressed highest,followed by Ml TPS5,Ml TPS6 and Ml TPS7.Ml TPS8,as well as Ml TPS3,were expressed at relatively low levels throughout the process.The expression level of Ml TPS1 was significantly increased at the early stage of the second flower bud differentiation,namely flower induction stage(S1 vs S4).Ml TPS1 was cloned with an ORF length of2793 bp,and it had two conserved protein domains:Glycosyltransferase family 20 Domain and trehalose-phosphatase Domain.The homology of Ml TPS1 gene to Arabidopsis thaliana and Populus euphratica was 73.54% and 77.6%respectively.The phylogenetic tree analysis showed that Ml TPS1 was closely related to Nelumbo nucifera,but far related to Capsicum annuum and Petunia hybrida.