Physiological controls of chrysanthemum DgD27 gene expression in regulation of shoot branching.

KEY MESSAGE: DgD27 was cloned from D. grandiflorum for the first time and played an important role in shoot branching of chrysanthemum. Shoot branching plays an important role in determining plant architecture. D27 was previously proven to be involved in the strigolactone biosynthetic pathway in rice, Arabidopsis, and Medicago. To investigate the role of D27 in shoot branching of chrysanthemum, we isolated the D27 homolog DgD27. Functional analysis showed that DgD27 was a plastid-localized protein that restored the phenotype of Arabidopsis d27-1. Gene expression analysis revealed that DgD27 was expressed at the highest levels in stem, and was up-regulated by exogenous auxin. Decapitation could down-regulate DgD27 expression, but this effect could be restored by exogenous auxin. DgD27 expression was significantly down-regulated by dark treatment in axillary buds. In addition, DgD27 transcripts produced rapid responses in shoots and roots under conditions of phosphate absence, but only mild variation in responses in buds, stems, and roots with low nitrogen treatment. DgBRC1 transcripts also showed the same response in buds under low nitrogen conditions. Under phosphate deficiency, indole-3-acetic acid (IAA) levels increased, zeatin riboside levels decreased, and abscisic acid (ABA) levels increased in the shoot, while both IAA and ABA levels increased in the shoot under low nitrogen treatments. Gibberellin acid levels were unaffected by phosphate deficiency and low nitrogen treatments. Taken together, these results demonstrated the diverse roles of DgD27 in response to physiological controls in chrysanthemum shoot branching.