Involvement of cytokinin response regulator RhRR1 in the control of flowering

Flowering at a suitable time is critical for ensuring reproductive success in the plant life cycle. The transition from vegetative growth to reproduction development is finely tuned by environmental and endogenous signals. To date, control of flowering involves five genetically defined pathways. However, the role of type-A response regulator genes in regulation of this process remains largely unclear. In the present study, we cloned and characterized a type-A response regulator gene (RhRR1) in rose. The expression of RhRR1 significantly increased in axillary bud during the transition from the vegetative growth to the start of floral differentiation, and in rose flowers in response to exogenous cytokinin or 1-methylcyclopropene (1-MCP) treatments, while that expression was markedly repressed by ethylene treatment. RhRR1 has the highest degree of sequence homology to AtARR8 and AtARR9, and is localized in the nucleus. Ectopic expression RhRR1 in Arabidopsis promoted early flowering, accompanied with the less rosette leaf number at bolting, and shorter bolting time after transferring the plants into pots. In addition, the expression of flowering regulatory genes in RhRR1 transgenic Arabidopsis, including FLOWERING LOCUS D, GA REQUIRING 1, LUMINIDEPENDENS, LEAFY, and TWIN SISTER OF FT clearly increased. These results allow us to infer that RhRR1 plays a key role in the control of flowering.