Shoot branching plays an important role in determining plant architecture. Strigolactones (SLs) negatively regulate shoot branching, and can respond to conditions of low or absent
phosphate or
nitrogen. The D14 gene is a probable candidate as an SL receptor in rice, petunia, and Arabidopsis. To investigate the roles of D14 in shoot branching of chrysanthemum, we isolated the D14 homolog DgD14. Functional analysis showed that DgD14 was a nuclear-localized
protein, and restored the phenotype of Arabidopsis d14-1. Exogenous SL (GR24) could down-regulate DgD14 expression, but this effect could be overridden by apical
auxin application.
Decapitation could down-regulate DgD14 expression, but this effect could be restored by exogenous
auxin. In addition, DgD14 transcripts produced rapid responses in shoot and root under conditions of
phosphate absence, but only a mild variation in bud and stem with low
nitrogen treatment. Indistinct reductions of P levels in shoot were observed in plants grown under low
nitrogen conditions. The absence of
phosphate and low levels of
nitrogen negatively affected plant growth. These results demonstrate that P levels in shoot had a close relationship with
phosphate, whereas
nitrogen did not directly regulate DgD14 expression in shoot. Taken together, these results demonstrated that DgD14 was the functional
strigolactone signaling component in chrysanthemum.