NtBRC1 suppresses axillary branching in tobacco after decapitation.

Axillary branching is controlled by a very complex mechanism involving various endogenous and environmental factors. Previous studies have shown that Tb1/BRC1 is the point of integration in the network of molecular mechanisms regulating axillary branching in plants. In this study, we cloned the Tb1/BRC1 ortholog, NtBRC1, from Nicotiana tabacum and functionally analyzed its role in the control of axillary branching in tobacco. Overexpression of NtBRC1 resulted in significant retardation of axillary branching, and downregulation of this gene resulted in significant acceleration of axillary branching after decapitation. This indicates a negative role for this gene in the regulation of axillary branching. In-line with previous reports, NtBRC1 was found to be expressed predominantly in axillary buds. Additionally, as expected, expression was decreased 8 h following decapitation, which further confirms its role in the suppression of axillary branching. Furthermore, the expression of NtBRC1 was significantly downregulated by cytokinin, but was not affected by GR24, a synthetic strigolactone. Based on the data collected in the present study, we demonstrate that NtBRC1 negatively regulates axillary branching in tobacco after decapitation and functions downstream of the cytokinin signaling pathway inside axillary buds.