Cucumber Strigolactone Receptor CsDAD2 and GA3 Interact to Regulate Shoot Branching in Arabidopsis thaliana L.

Previous studies identified that strigolactones (SLs) and gibberellins (GAs) interacted when controlling branching in plant shoots, but the underlying mechanism remains unknown. qRT-PCR analysis suggested that the SL receptor gene CsDAD2 was significantly upregulated in the leaves, stems, and nodes of cucumber after treatment with 50 mg/L of GA3. Furthermore, the CsDAD2 gene was cloned and introduced into wild-type Arabidopsis plants via Agrobacterium-mediated transformation. For the CsDAD2-OE lines, the endogenous content of GA3 was subsequently higher at the seedling stage, with the number of primary cauline branches also significantly increased at the maturity stage compared with WT. Additionally, GA-related genes were up-regulated in the first inter-nodes and the third nodes of the CsDAD2-OE lines, thus indicating that GA was metabolically active in these tissues. The expression of the branch inhibitor gene AtBRC1 decreased at the seedling stage as well as at the maturity stage of the CsDAD2-OE lines. These findings suggest that CsDAD2 might have important functions in the interactions between GAs and SLs as it can promote the accumulation of GAs in plant nodes and suppress the expression of BRC1, hence increasing primary cauline branching.