Cloning And Functional Analysis Of The Cucumber ACO2 And SCL1 Genes

Cucumber(Cucumis sativus)is a widely cultivated vegetable crop,and a typical monoecious species.The formation of unisexual flowers results from the selective arrest of the development of either staminate or pistillate primordia just after the bisexual stage.This process is defined sex determination,and the involved molecular factors have been identified in cucumber and watermelon,including four 1-aminocyclopropane-l-carboxylate synthases(ACS)that catalyzes the rate-limiting step in ethylene biosynthesis.ACC oxidase(ACO)converts ACC into ethylene;however,it remains elusive which ACO gene in the cucumber genome is critical for sex determination.We discovered that mutation in an ACO gene,CsAC02,confers androecy in cucumber that bears only male flowers.The mutation disrupts the enzymatic activity of CsAC02,resulting in 50%less ethylene emission from shoot tips.Ethylene promotes the formation of female flowers;the reduced ethylene emission fails to induce the female flowers,resulting in the formation of male flowers in the AC02 mutant.Plant species exhibit substantial variation in leaf morphology.We isolated a recessive mutant gene in cucumber that causes a significant decrease in the length and width of the leaf blade and loss of the typical auriculate leaf base and protruded middle margin.The mutant locus was termed small and cordate leaf 1(scl1).Microscopic analysis indicated that the scl1 mutant had fewer epidermal pavement cells in the leaves.Whole-genome resequencing of bulked segregants and genetic analysis revealed a single nucleotide polymorphism that was associated with the leaf phenotype.The causative SNP occurred in a putative nucleoside bisphosphate phosphatase,which was expressed in multiple organs.RNA-seq analysis of the wild type and scl1 mutant leaves suggested that SCL1 regulation may not involve known hormal pathways.Our work identified a candidate gene for SCL1 that may play a role in leaf development.