Preliminary Study On The Regulation Of Cucumber（cucumis Sativus L.）branch Development By Interaction Between Strigolactone And Gibberellin

Plant branching development is regulated by internal and external factors together,which plant hormones play important roles.Strigolactone（SL）is a new plant hormone,which is mainly synthesized in roots and transported from the lower end of morphology to the upper one,thus inhibiting plant branching.Gibberellin（GA）is also closely related to plant branch development,but the regulation on plant branch is different according to plant species.SL and GA have similar signaling pathways,both of which useα/βhydrolase derivatives as receptors,and there may be interactions between them.In this paper,two cucumber cultivars with different branching phenotypes（Much branching’Lvjian’;Less branch’Xinjian’）as the test materials,differentially expressed genes related to SL and GA were screened out after cucumber plants were treated with GA₃ and GR24.Bioinformatics and Arabidopsis genetic transformation methods were used to preliminarily analyze the function of target genes in plant branching.The results are as follows:1.Compared with the control,the plant height of cucumber’Lvjian’and’Xinjian’increased significantly after spraying GA₃ or GR24.The branch number of’Xinjian’decreased while that of’Lvjian’increased,after spraying GA₃ solution.The number of branches of the two cucumber species generally decreased after spraying GR24 solution.Exogenous GA₃ increased the expression levels of SL-related CsMAX1 and CsD14 genes in cucumber leaves and roots.The expression of GA-related genes in cucumber were generally decreased after GR24 application,and the expression of CsGA3ox1 decreased with the increasing of SL concentration.These results suggested that SL inhibits the branching development of cucumber,while the effects of GA on the branching development of cucumber vary with genotype,and the genes CsMAX1,CsD14 and CsGA3ox1 may be involved in the cross interaction between SL and GA.2.Tissue localization analysis showed that CsMAX1 was mainly expressed in roots,cotyledons,leaves,rosette base,leaf axils and fruit stalks,and mainly concentrated in vascular tissues,indicated that CsMAX1 might play certain functions in these parts.CsD14 was mainly expressed in roots,cotyledons and mature leaves.CsGA3ox1 was mainly expressed in cotyledons,young leaves,mature leaves and fruits with vigorous cell division,indicated that it might be involved in GA synthesis pathway in these parts.3.The c DNA lengths of CsMAX1,CsD14 and CsGA3ox1 were 1620 bp,908 bp and 1125bp,encoding 529,266 and 374 amino acids,respectively.CsMAX1 is a cytochrome P450family gene.Its encoding protein is a stable,hydrophilic,transmembrane protein,which is predicted to be located in the cytoplasmic membrane by subcellular localization.The promoter region contains GA response elements.CsD14 belongs to theα/βhydrolase family and is a stable hydrophobic protein,which is predicted to be located in the cytoplasm by subcellular localization.CsGA3ox1 belongs to the 2-oxyglutarate/Fe（II）-dependent dioxygenase family of genes and is a stable hydrophilic protein predicted to be located in the cytoplasm by subcellular localization.4.Overexpression vectors of CsMAX1,CsD14 and CsGA3ox1 were constructed and transformed into Arabidopsis thaliana.Transgenic Arabidopsis thaliana showed significantly increased branch number,compared with WT.In CSMAX1-OE lines,GA synthesis pathway genes and signal transduction genes were up-regulated in most tissues,and GA₃ content was significantly increased.The positive regulation genes of plant branches were generally increased in all tissues.It was speculated that CsMAX1 promoted GA effect in Arabidopsis thaliana,and thus promoted the increase of branching.In CsD14-OE lines,the expression level of GA-degrading genes in all tissues were extremely significantly decreased and the content of GA₃ increased,but the expression level of GA signal transduction gene was generally decreased in all tissues,the expression level of positive branch regulation gene was generally up-regulated in all tissues,and the branch inhibition gene At BRC1 was down-regulated in all tissues.In CsGA3ox1-OE lines,the increased GA₃ content generally increased the expression level of SL-related genes and genes promoted branching development in each tissue.Therefore,it is speculated that GA not only promoted signal transduction of SL,but also might have a certain effect on other signals promoting branching.