Interaction Of SL Transduction Gene CsDAD2 And GA₃ In Regulation Of Cucumber Branch Development

In order to survive and reproduce,plants need to adapt to changes in various environments.Branching is one of the life activities that regulates and optimizes plant phenotypes.Strigolactone（SL）is a plant hormone found in recent years,which has the effect of inhibiting plant branching.Gibberellin（GA）has also been found to be involved in the regulation of bud growth,and may interact with SL in regulating the growth of axillary buds.Cucumber is an important vegetable crop in China,and its yield is affected by the number of lateral branches.In order to investigate the interaction between SL and GA on cucumber branches,this study treated cucumber with GA₃ to detect the expression changes of related genes in cucumber.At the same time,the SL-related gene CsDAD2 was cloned,an overexpression vector was constructed,and a transgenic Arabidopsis strain was harvested,and its related phenotype and related gene changes were detected.This provided research directions and theoretical support for improving the mechanism of plant hormone interactions and regulating the growth of cucumber lateral branches.The main results obtained are as follows:（1）GA₃ treatment reduced the expression of SL synthesis gene CsCCD7 in cucumber leaves and roots,and promoted the expression of CsCCD7 in leaf axils.The SL signal pathway genes CsD14 and CsDAD2 in cucumber stem and leaf axilla were significantly increased after GA₃ treatment,and the changes of CsDAD2 in leaf axilla were more obvious.GA₃ also promoted increased expression of the recording factor CsTCP2 and the branch inhibitor CsBRC1.These suggested that GA₃ promoted the transduction of SL signals and has an inhibitory effect on the branching of cucumber.（2）The real-time quantitative PCR was used to investigate the expression of CsDAD2 gene tissues,which showed that CsDAD2 was expressed in cucumber roots,stems,leaves,leaf axils and cotyledons,with the highest expression in roots.GUS staining of the promoter also demonstrated that CsDAD2 gene was significantly expressed in leaves,leaf axils and roots.（3）The CsDAD2 gene of cucumber was cloned.Bioinformatics analysis showed that the protein encoded by this gene was soluble protein,consisting of 276 amino acids,and it did not belong to the category of secreted proteins and transmembrane proteins.The protein had a homologous relationship and evolutionary relationship with wild strawberry,red willow,grape,etc.Promoter sequence analysis indicated that the gene may be involved in the interaction between light response and hormones.（4）A CsDAD2 overexpression vector was constructed and introduced into Arabidopsis thaliana by inflorescence infection.The CsDAD2 overexpression transgenic Arabidopsis plants were obtained by screening and cultivation.Real-time quantitative PCR showed that the expression of GA metabolic genes was reduced and the expression of GA signal pathway genes was increased in transgenic Arabidopsis seedlings.In the transgenic Arabidopsis plants,the expression of GA metabolic genes in various tissues also decreased,and the signal pathway genes increased in the leaf axils.It was speculated that there is an interaction regulatory pathway between SL and GA signaling pathway mediated by CsDAD2.The difference in the expression of branch suppression gene AtBRC1 might be one of the reasons for the branch change of transgenic Arabidopsis thaliana.The above results further showed that SL and GA do have the possibility of interactive regulation in plant branching,and seem to involve more complex internal signal operations.