Analysis Of Papaya Sex Differentiation And The CpSVP Gene

Carica papaya L.is a common tropical fruit.It is also known as the model plant to study sex chromosome evolution in angiosperms,due to its nascent origin.Papaya has three sex types:XX chromosome type as female,XY chromosome type as male plants,and XYh chromosome type as hermaphrodite.Papaya X and Y chromosomes(or X and Yh chromosome)sequence similarity is about 85%,whereas Y and Yh chromosome have 99.6%similarity.Papaya CpSVP gene is absent in the X chromosome,and CpSVPY allele and CpSVPYh allele structure were different.The CpSVP gene is the only one which was tested differentially expressed genes of Y chromosome and Yh chromosome.Previous studies predicts that CpSVP gene of papaya cause sex differentiation because the gene is Y(or Yh)chromosome specific gene.My study is comprised of two parts:one part is to summarize the papaya sex differentiation by morphological observations;the other part consists of papaya CpSVP genes analysis and transformation tests.The purpose of my study was to explore the relationship between sex differentiation and papaya CpSVP gene.The key results obtained are as follow:1.Based on flower morphology observations,ten developmental stages were defined in male flowers and six stages were defined in female flowers,and ten stages were defined in hermaphrodite flowers.From morphological observations of flower developmental stages,we can find reference for studies about papaya sex differentiation at molecular mechanism.2.It reveled that there were two copies papaya CpSVP genes expressed in three forms:CpSVP gene an autosome(CpSVPA gene),a pair of CpSVP allele on the Y chromosome(CpSVPY gene)and Yh chromosome(CpSVPYh gene).Compared CpSVPY and CpSVPYh allele structure,a MADS domain was absent from CpSVPYh.CpSVPA gene and CpSVPY gene sequence similarity was 94%;it is predicted that they may be functionally redundant.Through the CpSVP genes transcriptome analysis,it was observed that CpSVPY and CpSVPYh shown opposite expression pattern in different sizes of flowers.Papaya CpSVPY expressed on a high level,lower in leaves,while CpSVPYh has lower expression in flowers,but high in leaves.Furthermore,analysis of CpSVPY and CpSVPA expression during the stamen development was conducted;CpSVPY was highly expressed in mature stamens and mainly concentrated in the anthers.3.There is no abnormal phenotype observed when CpSVPY is ectopic expressed in Arabidopsis thaliana.At the same time,Agrobacterium mediated callus transformation was carried out.It was concluded that Agrobacterium treated callus survival ratio and efficiency of resistant callus differentiation were the key factors for successful papaya callus Agrobacterium transformation.Sex determination has been the one of the focus of biological researches.Especially for papaya.As an economic crop,sex determination study is directly related to the yield.The most significant phenotypic differences of papaya sex differentiation are floral structure and long peduncle,which is Y-linked inheritance phenotype.Either of them will change the papaya plant architecture.Recently genomic analyses focused on the predicted candidate genes in sex determining region of the Y chromosome.Further testing of gene’s functions is going.