Molecular Mechanism Of CsFUL Regulating Fruit Development In Cucumber

The fruit is developed from the ovary or other parts of the flower after pollination and fertilization of the carpel.The fruit can be grouped into dry fruit and fleshy fruit.Cucumber(Cucumis sativus L.)fruit belongs to pepo in the fleshy fruit,and develops from the inferior ovaries of three fused carpels.Cucumber fruit can be used as fresh product or processed into pickles,and is of important economic and nutritional value for human beings.Till now,fruit development research focuses on the silique development in model plant Arabidopsis and the berry fruit in tomato,but little is known about the pepo fruit development such as that in cucumber.Thus,here we used the monoecious cucumber as materials,utilized techniques and methods in molecular biology?biochemistry and developmental biology,explored the biological function and molecular mechanism of CsFUL during cucumber fruit development through gene cloning,expression analysis and functional characterization,The main results are as follows:1?There are two FUL homologous genes in cucumber,CsFUL1(Csa004592)and CsFUL2(Csa004120),which belong to the MADS-box transcription factors.Expression analysis showed that CsFUL1 and CsFUL2 were mainly expressed in the reproductive organs and displayed the highest expression in male flowers.In situ hybridization showed that CsFUL1 and CsFUL2 were expressed in the shoot apical meristem(SAM),floral primordium and early stage of fruit development.GUS staining assay indicated that CsFUL1 was specifically expressed in the stamen filaments?the top and base of carple as well as the carpopodium.Subcellular localization analysis showed that both CsFUL1 and CsFUL2 were located in the cell nucleus.2?Ectopic expression of CsFUL1 and CsFUL2 in Arabidopsis showed that CsFUL1/2 specifically regulated stamen numbers and fruit length,however,ectopic expression of CsFUL1 or CsFUL2 could not rescue the phenotypes of Arabidopsis ful-Imutant,suggesting that the function of CsFUL1/2 were not conserved.3?Genetic transformation analyses in cucumber showed that overexpression of CsFUL1 resulted in increasing number of petals and stamens in male flower,as well as short and stubby fruits.Transcriptome analysis of the CsFUL1 overexpression lines indicated the CsFUL1 might regulate cell cycle related genes to control cell division and expansion,and thus the final fruit length in cucumber.Moreover,CsFUL1 might regulate cucumber fruit development together with additional transcription factors.4?Down-regulation of CsFUL2 by RNAi mainly affected female organ development,resulted in increasing number of petals in the female flower and ventricles in the fruit.5?Transcriptome analyses of the young fruits from two high generation recombinant inbred lines with different fruit length showed that CsFUL1 was significantly upregulated in the line 408 with long fruit as compared to that in line 409,suggesting that CsFUL1 may be a negative regulator functions in cucumber fruit length control.As such,this study uncovered the biological function of CsFUL during flower and fruit development in cucumber,as well as elucidated the molecular mechanism of CsFUL,which enriched the theory of fruit development in cucumber,and provided the molecular guidance for breeding of cucumber varieties with optimum fruit length.