Cytokinin Type-B Response Regulators Promote Bulbil Initiation in .

The bulbil is an important vegetative reproductive organ in triploid whose 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-B s, , , , and , in for the first time. The five s 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-B s are involved in bulbil formation in a functionally redundant manner and can activate expression. In summary, our study elucidates the process by which cytokinins regulate bulbil initiation in through type-B LlRRs and lays a foundation for research on the molecular mechanism of bulbil formation in the lily.