Anatomical Analysis During Fruit Development And Isolation Of Fruit Shaping-related Gene In Vaccinium Corymbosum

Blueberry is one of high-economic-value crop,which fruit is deeply popular with consumers.The indexes affecting fruit quality,such as size,shape,pulp texture,fruit flavor,maturity,were different in wide variation of blueberries.Recently,the research of blueberry mainly focuse on synthesis and regulation of anthocyanin,fruit quality of mature fruit,fruit storage and breeding new varieties,and little attention on fruit development and fruit morphology.Understanding blueberry fruit development and fruit morphology development rhythm would provide important direction to farm management and cultivation of new varieties.In this study,round and large fruit cultivar Brigita,flat-round and large fruit cultivar O’Neal as well as round and small fruit cultivar Bluerain were used.By measuring fruit growth curve,including the transverse diameter,longitudinal diameter,fruit weight,tissue paraffin section,isolating and expression analysis of fruit shape-related genes VcFAS,VcSUN and VcOVATE,fruit development rhythm and reasons for the differences in the formation of fruit shape in three V.corymbosum cultivars.The results are as follows:（1）According to developmental rhythm of flower bud expansion stage and weight growth curve in three cultivars blueberries,the flower bud expansion stage was divided into 6 stages:I-S0,and fruit development after flowering was divided into S1-S6.Weight growth curve of three cultivars blueberries showed a double sigmoid growth pattern growth with two rapid growth periods.The trend of transverse diameter,longitudinal diameter,vertical section area and fruit shape index in three V.corymbosum cultivars are similar.After counting the number of transverse and longitudinal cells in I-S6,the pulp cells were found in progress of transverse division and longitudinal division in three V.corymbosum cultivars.The pulp cells mainly divided longitudinally and the transverse division was relatively weak.At the early stage of fruit development（S0-S1）,cell division was intense.From S1 phase,the cells expand rapidly,and continued to S6 phase.Although the development tendency is consistent,fruit and morphological development in three V.corymbosum cultivars also existed obvious differences.Bell flower of Bluerain obviously was smaller than O’Neal and Brigita.The two rapid growing stages of fruit development of Bluerain were shortest,and it development phases were slower than O’Neal and Brigita obviously.Moreover,in the two rapid growing stages of fruit development,especially in the second rapid growing stages,O’Neal grew slower than Brigita evidently.The longitudinal division in the three V.corymbosum cultivars were obvious differences during S1-S6.After S1 stage the longitudinal cells of pulp of Bluerain ceased to divide,while the longitudinal cells of pulp of O’Neal and Brigita still continued to divide.Maybe it is the important reason caused the differences of fruit size and shape among V.corymbosum cultivars O’Neal,Brigita and Bluerain.（2）VcFAS,VcSUN and VcOVATE gene were successfully isolated.in three V.corymbosum cultivar O’Neal,Brigita and Bluerain.Bioinformatic analysis showed that single nucleotide polymorphisms（SNPs）were presented in the three genes of three blueberry cultivars.There were five introns in the.VcFAS gDNA,and long insert/deletion fragments were existed in the 1st,2nd and 5th introns,while four and none introns were existed in the gDNAs of VcSUN and VcOVATE,respectively.Sequence alignment analysis showed that the similarities of VcFAS,VcSUN and VcOVATE with Vitis vinifera YABBY 2 isoform X4（XP₀10651638）,Vitis vinifera IQ-DOMAIN 1-like（XP₀02277151）and Pyrus bretschneideri OFP7（XP₀09371567）were 76%,50%and 54%,respectively.The expression levels of VcFAS,VcSUN and VcOVATE were relatively high in the flower bud enlargement stages of Bluerain and the 1st rapid growth stage of fruits of O’Neal and Brigita.Our results showed that the gene expression profiles of VcFAS and VcSUN were consistent with the growth curves of fruit horizontal diameter as well as average fruit weight,and VcFAS and VcSUN were presumed as the genes that regulate blueberry fruit shape and size.Moreover,flower bud enlargement stage and the 1st rapid growth stage of fruits were the critical periods which affected the fruit shape and size.