Fine Mapping Of Subgynoecious QTLs In Cucumber And The Roles Of AP3 Orthologue Genes In Cucurbits Sex Determination

Cucumber(Cucumis sativus L.)is the second largest protected vegetable crop in China.It has been a model plant to study the mechanism of sex determination in flowering plants due to its diverse sex types.The development of cucumber unisexual flower is influenced by genetic,environmental and hormonal,of which ethylene is called sex hormone of cucumber,which promotes female flower development.Due to unsatisfactory cultivation conditions such as water and fertilizer management in cucumber cultivation in China,the phenomenon of abortion and abnormal fruits often occurs in gynoecious variety,which affects the economic value of cucumber.However,dominant subgynoecious varieties can significantly increase female flower rate and avoid abnormal fruits while increasing yield.Therefore,breeding subgynoecious varieties is an important way to develope fine cucumber varieties.Previously,we have already mapped the major QTL on chromosome 3 in the F2 and BC8S1 populations of S-2-98(subgynoecious)and 95(monoecious)by using 2112 cucumber SRR markers and dCAPS/CAPS markers developed based on parental differences.The major QTL contributed to 54.6%of the phenotypic variation.In this study,we carried out fine mapping the major QTL of subgynoecious on above plant materials and obtained the following results 1 and 2.ABC model of flower development based on Arabidopsis thaliana and Antirrhinum majus promoted the research on flower development of angiosperms,but few studies were reported on the development process of Cucurbits unisexual flowers.Study the regulation mechanism of ABC model in the unisexual flowers development of Cucurbits has important scientific and practical significance.Previous study demonstrates that CsAP3,the B class floral organ identity gene in cucumber,participate in the process of stamen arrest in cucumber female flower by regulating the expression of ethylene receptor CsETR1.To further understand the conserved mechanism of the role of ethylene in stamen arrestment,in this study,AP3 homologue genes in Momordica charantia,Luffa cylindrical,Cucumis melo,Citrullus lanatus,Cucurbita maxima and Cucurbita pepo were analyzed and obtained the following results 3 and 4.1.Using the heterozygous plant DE408-24H-1-20 in the BC8S2 population and the recombinant plants DE408-24Re-56,DE408-24Re-82,DE411-Re23-25 to construct a genetic population,and 7 effective recombinant plants were determined according to Kompetivive Allele Specific PCR(KASP)typing and phenotype investigation results.Using these 7 recombinant plants,the major QTL was narrowed to 52 kb.Two candidate genes were identified by analyzing the expression level of genes in the 52 kb by transcriptome analysis and qPCR experiment.2.Candidate gene-edited plants were obtained by the CRISPR/Cas9 system.3.Unlike other plants,there are non-synonymous mutations in the coding region of the short GV repeats in the C-terminus of AP3 protein in Cucurbits.4.Electrophoretic mobility shift assay(EMSA)and dual luciferase transient expression assay in tobacco leaves showed that,the AP3 homologous proteins of melon,watermelon and pumpkin have potential to bind the ETR1 promoter and positively regulate the ETR1 homologous gene in the corresponding species.The edible organ of cucumber is fruit,which is developed from female flowers.Therefore,it is of great significance to study the mechanism of dominant subgynoecious in cucumber to improve yield.Cucurbits contains a variety of vegetables and fruits,and their edible organ are developed from female flowers.Studying class B gene AP3 in ABC model on the development of unisexual flowers enriches the theory of flower development in Cucurbits.