Functional Dissection Of BR Signal Transduction In Regulating Tomato Fruit Shape

Tomato(Solanum lycopersicum)is not only a significant horticultural crop,providing abundant nutrients for human,but also one of the model plants for the research on fresh fruits.As an important agronomic trait,tomato fruit shape is the essential goal for modern tomato breeding.At present,the genes,cloned by QLT controlling the tomato fruit shape,are OVATE,SUN,and OFP20.Fas and LC,cloned by regulating the tomato locus,can also influence the tomato fruit shape.BR and GA are two kinds of vital hormones in plant growth and development,but their specific effects on tomato fruit shape remain unclearly.In this study,with the method of increasing the BR and GA signal in tomato,we found that both BR and GA can influence the tomato fruit shape.Based on the signal transduction of BR and GA,we proved that SlGSK4 and SlDELLA,named as PROCERA,played important roles in tomato fruit shape control,and identified a plant-special transcription factor;SlGRF1.SlGRF1 can interact with SlGSK4 and PROCERA,and regulate tomato fruit shape.The main results are as follows:1,Increasing the BR signal with the method of spaying BR or enhancing the expression of DWARF,which play key roles in BR biosynthesis,made tomato fruit shape elongated.2,Suppressing the BR signal led to much flatter tomato fruit.SlGSK4 is an orthologous gene of BIN2,a negative regulator in Arabidopsis BR signal transduction.In tomato,increasing the expression of SlGSK4 resulted in much flatter tomato fruit.3,After treating with GA,tomato were parthenocarpy and we got the elongated fruit shape tomato.When we mutated PROCERA,a protein in GA signal transduction,tomato also showed the phenotype of parthenocarpy and elongated tomato fruit.4,Screening the cDNA library using the SlGSK4 as bait,we found its interacting protein SlGRF1.We convinced that SlGSK4 interacted with SlGRF1 by pull-down assay and these two proteins had the opposite function in tomato fruit shape.In the yeast,SlGRF1 interacted with PROCERA and PROCERA may suppress SlGRF1.5,SlGRF1,a plant-special transcription factor,has self-activating activity.SlGRF1 was regulated by miR396.We cannot detect SlGRF1 protein,but we can detect Slr GRF1 protein,with the synonymous mutation in the sequence of the target of miR396 to SlGRF1.Slr GRF1 protein localized in the nucleus.We overexpressed SlGRF1,and the tomato fruit shape was elongated.SlGRF2 and SlGRF3,the subfamily of SlGRF1,displayed the same function on tomato fruit shape,indicating SlGRF1 was functional redundancy in tomato fruit shape.6,The difference in the number of cell layer and the cell size resulted in the changes in fruit shape between SlGSK4-OE and SlGRF1-OE plants.Tomato fruit of SlGSK4-OE owned more numbers of cell layer and less size of the cell,which was opposite in SlGSK1-OE plants.7,In the SlGRF1-OE and SlGSK4-OE plants,the expression of OVATE,SUN,and OFP20 showed no significant changes.And in the OVATE-CR plants,the expression of SlGRF1 and SlGSK4 also displayed no significant differences.The results indicated that SlGRF1 may control the tomato fruit shape independent of OVATE,SUN and OFP20 pathway.