Abstract

The bulbil is an important vegetative reproductive organ in triploidLilium lancifoliumwhose development is promoted by cytokinins. Type-B response regulators (RRs) are critical regulators that mediate primary cytokinin responses and promote cytokinin-induced gene expression. However, the function of cytokinin type-B Arabidopsis RRs (ARRs) in regulating bulbil formation is unclear. In this study, we identified five type-BLlRRs,LlRR1,LlRR2,LlRR10,LlRR11andLlRR12, inL. lancifoliumfor the first time. The fiveLlRRs encode proteins of 715, 675, 573, 582 and 647 amino acids. All of the regulators belong to the B-I subfamily, whose members typically contain a conserved CheY-homologous receiver (REC) domain and an Myb DNA-binding (MYB) domain at the N-terminus. As transcription factors, all five type-B LlRRs localize at the nucleus and are widely expressed in plant tissues, especially during axillary meristem (AM) formation. Functional analysis showed that type-BLlRRs are involved in bulbil formation in a functionally redundant manner and can activateLlRR9expression. In summary, our study elucidates the process by which cytokinins regulate bulbil initiation inL. lancifoliumthrough type-B LlRRs and lays a foundation for research on the molecular mechanism of bulbil formation in the lily.Keywords:Lilium lancifolium;cytokinin;bulbil formation;type-B response regulators