Preliminary Study On The Bud Differentiation Of Single-flowered And Lateral-flowered Tree Peony Cultivars

As a traditional ornamental plant,tree peony?Paeonia suffruticosa?is deeply loved because of its grace,dignity and dignity.While,the short and concentrated florescence casues great restrict to it's development.How to extend the florescence has been a problem that researchers have been devoting to.Most tree peony cultivars have only one flowers in one flowering branch,while a few cultivars have multi-flowered branches,and the flowering dates of these flower are not synchronized.The top flower bloom before the lateral flower.The lateral flowers increased the flower amount on a plant,and also extended the florescence.In this paper,the flower bud differentiation of single-flowered cultivars and latera-flowered cultivars were studied.Through morphological observation and physiological research,combined with the transcriptome comparative analysis method of the lateral bud differentiation stage,preliminary understanding the physiological change during flower bud differentiation process between latera-flowered cultivars‘Zimei Youchun'and single-flowered cultivars‘Lihua Fen'.The differences and similarities of flower bud differentiation between two cultivars were compared,combing with transcriptome analysis of the lateral bud differentiation stage of P.suffruticosa'Zimei Youchun',screening differentially expressed genes related to carbohydrates and hormones,and performing functional enrichment analysis.The specific results are as follows:1)The flower bud differentiation of P.suffruticosa'Lihua Fen'can be divided into 6 periods:leaf primodium differentiation stage?LP??bract primodium differentiation stage?BP??sepal primodium differentiation stage?TSe P??petal primodium differentiation stage?Pe P??stamen primodium differentiation stage?SP??pistil primodium differentiation stage?PP?.The flower bud differentiation of P.suffruticosa'Zimei Youchun'and other latera-flowered cultivars can be divided into 11 periods:leaf primodium differentiation stage?LP?,top flower bract primodium differentiation stage?TBP?,top flower sepal primodium differentiation stage?TSe P?),Top flower petal primodium differentiation stage?TPe P?,top flower stamen primodium differentiation stage?TSP?,top flower pistil primodium differentiation stage?TPP?,lateral flower bract primordium differentiation stage?LBP?,lateral flower sepal primordium differentiation stage?LSe P?,lateral flower petal primodium differentiation stage?LPe P?,lateral flower stamen primodium differentiation stage?LSP?,lateral flower pistil primordium differentiation stage?LPP?.There are difference in the initial time,the top flower primodium differentiate first,and the lateral flower primodium differentiate later.Compared with the top flower,the differentiation time of bract primodium of lateral flower is greatly extended,P.suffruticosa'Zimei Youchun'was extended 31 day,P.suffruticosa'Yune Fen'was extended 22 day,the differentiation period of lateral flower bract primodium synchronized with petals?stamens and pistil primordium differentiation of top flower,after the top flower differentiation was basically completed,the lateral flower quickly completed the differentiation of sepal,stamen,pistil and other floral primordium,compared with the single-flowered cultivars,the latera-flowered cultivars has at least one more flower,the differentiation lasted longer.2)The soluble sugar content in the leaves of single-flowered cultivars and latera-flowered cultivars both showed a decrease-increase trend in the flower bud differentiation process.Whether single-flowered cultivars or latera-flowered cultivars,with flower bud differentiation progresses soluble sugar content decreased,the accumulation of soluble sugar may promoting the differentiation of flower buds of P.suffruticosa.The soluble starch in the leaves of P.suffruticosa'Zimei Youchun'showed an increase-decrease trend,while P.suffruticosa'Lihua Fen'had been in a decrease trend at the initial stage of flower bud differentiation.Starch may be an energy supplement in the process of flower bud differentiation.During the process of flower bud differentiation of P.suffruticosa'Zimei Youchun',the soluble protein content of the leaves showed an overall increase-decrease-increasing-decrease trend,P.suffruticosa'Lihua Fen'showed an increase-decrease trend,when the primodium differentiation of pistil and stamen,soluble protein content decreased significantly in P.suffruticosa'Lihua Fen',more protein may be needed for morphological development of pistils and stamens.3)Hormones play an important role in regulating flower bud differentiation.Higher levels of ABA,GA₃,ZRs and lower levels of IAA content may promoting the initiation of flower bud differentiation of P.suffruticosa,higher levels of ZRs,IAA and lower levels of ABA and GA₃may be beneficial to the differentiation of lateral flower primordium.4)Through comparative analysis of transcriptome differences when the latera flower primordium differentiation stage,total of 23988 differential genes were expressed in the initial stage of P.suffruticosa'Zimei Youchun'lateral flower primordium differentiation,including 13519 up-regulated genes,10469down-regulated genes,and 931 differential genes related to carbohydrates,there are 451 genes up-regulated and 480 genes down-regulated,among them,IAA synthesis related genes ILR1,YUC and transport related genes ABP,CTKs response factor ARR9,ABA synthesis related genes DCED1 and ABA metabolism related genes PYL4,ABAH,PYR1 and gibberellin oxidation genes GA3OX2,GA3OX3,GA3OX4 and gibberellin Synthetic related genes CPS all expressed differentially.Many genes related to branching are differentially expressed,such as transcription factors CUC1,BRC1,LOF1,auxin-related genes AXR1,YUCCA,and LAS genes that act on the initial stage of lateral meristems,which regulate the growth of lateral buds MAX1,MAX2,Genes such as RMS4 may have a greater correlation with the formation of side flower buds/side flower branches of Paeonia suffruticosa.