Cytokinin Type-B Response Regulators Promote Bulbil Initiation in Lilium lancifolium

Abstract

The bulbil is an important vegetative reproductive organ in triploid Lilium lancifolium 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 LlRRs, LlRR1, LlRR2, LlRR10, LlRR11 and LlRR12, in L. lancifolium for the first time. The five LlRRs 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 LlRRs are involved in bulbil formation in a functionally redundant manner and can activate LlRR9 expression. In summary, our study elucidates the process by which cytokinins regulate bulbil initiation in L. lancifolium through type-B LlRRs and lays a foundation for research on the molecular mechanism of bulbil formation in the lily.

Transcriptome Analysis Reveals the Molecular Regularity Mechanism Underlying Stem Bulblet Formation in Oriental Lily ‘Siberia’; Functional Characterization of the LoLOB18 Gene

“…Gravity regulates the transport and local accumulation of auxin [ 12 ]; thus, auxin acts as a crucial signal for lateral organ formation by inducing the expression of the LOB gene family [ 25 , 26 , 27 ]. In Arabidopsis , LOB and KNOX genes may interact with each other antagonistically to control lateral organ development [ 19 ]. Additionally, KNOX genes have been associated with organogenesis during bulblet formation, and it has been proven that LaKNOX1 interacts with LaKNOX2 and LaBEL1 to regulate stem bulblet formation in lily [ 16 ].…”

“…A. tumefaciens cells harboring TRV1 and TRV2:: LOB18 , TRV2 (as a negative control) were resuspended in induction medium at 1:1 ratio, OD 600 = 1. Stem segments of Lilium were surface sterilized with 75% alcohol and 10% NaClO and then cut into small stem segments for vacuum infiltration [ 19 ]. The infiltrated segments were washed with distilled water three times for 3 min each time and then grown on MS medium with 30 g/L sucrose and 6 g/L agar, PH 5.8, in the dark at 15 °C for 2 days, followed by growth at 22 °C under a 16/8 h light/dark cycle.…”

“…Several studies have revealed that genetic factors are critical for stem bulblet formation in lilies [ 7 ]. Type-B response regulators ( LIRRs ) are involved in bulbil formation in a functionally redundant manner and can activate LIRR9 expression [ 19 ]. The LlWOX9 and LlWOX11 genes have been shown to be positive regulators of bulbil formation.…”

Bulbil initiation: a comprehensive review on resources, development, and utilisation, with emphasis on molecular mechanisms, advanced technologies, and future prospects

“…This result is similar to that of the BR-induced increased cell wall glucose in switchgrass cell suspension cultures ( Rao et al., 2017 ). Sucrose can also induce the expression of WUSCHEL-related homeobox 11/9 (WOX 11/9) ( He et al., 2022 ), LlRR 1/2/9/10/11/12 ( He et al., 2021 , 2022 ), SUS , and SUCROSE TRANSPORTER 2 (SUT 2) , and WOX 11 is a transcription factor that can promote the regeneration of plant organs ( Wan et al., 2023 ), SUT 2 plays an important role in the transport process of sucrose ( Zhang et al., 2016 ). In addition to the two core modules of hormone and sugar, there are many unidentified genes involved in the regulation of bulbil development, for instance: GFLO ( Li et al., 2014 ; Xu et al., 2020 ; Zhang et al., 2023a ), KNOX1/2/6 ( Abraham-Juarez et al., 2010 ; Zhang et al., 2013 ; Peng, 2016 ), MADS1/2/4/6/7 ( Peng, 2016 ; Wu et al., 2019 ), LFY ( Peng, 2016 ), GRAS ( Peng, 2016 ), LOB ( Peng, 2016 ), F-box ( Peng, 2016 ), PteMFT ( Liu, 2018) , PEBP ( Liu et al., 2018 ), ARF ( Li et al., 2023b ), GFLO ( Wang et al., 2004 ), CCD8 ( Sun et al., 2011 ), IPT1 ( He et al., 2020 ), CKX4 ( He et al., 2020 ), LOG ( He et al., 2020 ), PIN ( Abraham et al., 2015 ).…”

Plant Cell and Organism Development 2.0

“…Based on the fact that in Lilium lancifolium, cytokinins can promote the initiation of an axillary meristem (AM) during the formation of bulbils, in their article, He et al [12] elucidate the function of the cytokinin type-B response regulators (RRs). Because of its triploid nature, this ornamental and medicinal lily is primarily propagated asexually via bulbils that originate from AMs.…”