Molecular Mechanism Of CsLFY-and CsTFL1 In Regulating Shoot Apical Meristem In Cucumber

Cucumber(Cucumis sativus L.)is an important vegetable crop that possesses two different types of growth habit:indeterminant growth and determinant growth.Most of cultivated cucumber has indeterminate growth habit,with long growth period and high yield.However,the cucumber with determinate growth habit is benificial for mechanically harvest and thus save manpower.The cucumber leaves are produced from the shoot apical meristem and unisexual flowers(including male and female flowers)are generated from the leaf axils.The female flowers develop into fruits.Maintainance of shoot apical meristem directly determines the indeterminate or determinate growth habit in cucumber.The flower integrator LFY of Arabidopsis and its homologs have been shown to play important roles in promoting flower development,flowering time and branching.Furthermore,previous studies have shown that the determinate growth in cucumber was controlled by a single recessive gene.In the cucumber inbred line G421(Gy7),the determinate growth habit was controlled by the de locus that was located in cucumber chromosome 6.In this study,we obtained CsLFY by homologous cloning and found that the de locus is caused by a non-synonymous SNP in CsTFL1 through map-based cloning.Using tools and methods of molecular biology,developmental biology and biochemistry,we explored the biological function of CsLFY and CsTFLl in cucumber.Major results were listed as followed:1.CsLFY was expressed in the SAM,floral meristem(FM)and floral organ primordia.Ectopic expression of CsLFY rescued the defective flower development phenotype of the lfy-5 mutant in Arabidopsis.2.Knockdown of CsLFY by RNAi led to defective shoot development and premature discontinuance of leaf initiation in cucumber.Transcription of CsWUS and putative CsLFY target genes including CsAP3 and CUM1 were significantly reduced in the CsLFY-RNAi lines.3.Biochemical analyses indicated that CsLFY physically interacts with CsWUS in cucumber.4.CsTFL1 is expressed in the subapical regions of the shoot apical meristem,lateral meristem and young stems.Ectopic expression of CsTFLl can delay the flowering time of Arabidopsis and rescue the terminal flower phenotype of the Arabidopsis tfl1-11 mutant.5.Knockdown of CsTFL1 by RNAi or point mutation 3579 resulted in determinate growth and formation of terminal flowers in cucumber.6.In cucumber,despite CsFD can bind to CsFT and two 14-3-3 proteins,no interactions were detected between CsTFL1 and CsFD or 14-3-3 proteins.In conclusion,CsLFY has a novel function in regulating shoot meristem maintenance through interaction with CsWUS,and promotes flower development via activation of CsAP3 and CUM1 in cucumber,which revealed the biological function and regulatory mechanism of the flower integrator CsLFY in regulating SAM maintenance and flower development in cucumber.In addition,CsTFL1 exhibited conserved functions in regulating the formation of terminal flower and determinate growth in cucumber,but with distinct working model as compared to TFL1 gene in Arabidopsis,which dissected the role and working model of CsTFLl in regulating terminal flower and determinant growth habit of cucumber.These results provide the theoretical basis and gene resources for cucumber breeding with optimum architechture targeting the need of different production systems.