Early Sucrose Degradation and the Dominant Sucrose Cleavage Pattern Influence Lycoris sprengeri Bulblet Regeneration In Vitro

Abstract

Bulblet formation and development determine the quantitative and qualitative traits, respectively, of bulb yield for most flowering bulbs. For Lycoris species, however, the underlying molecular mechanism remains elusive. Here, clonal bulblets of Lycoris sprengeri (Ls) derived from the same probulb were used as explants to establish efficient and inefficient in vitro regeneration systems by adjusting the 6-benzyladenine (BA) concentrations in media. BA application did not change the biological processes among groups but led to earlier decreases in sucrose and total soluble sugar (TSS) contents. Correlation analyses showed that the BA treatments changed the interaction between carbohydrate and endogenous hormone contents during bulblet regeneration. We found that two sucrose degradation enzyme-related genes, cell wall invertase (CWIN) and sucrose synthase, exhibited exactly opposite expression patterns during the competence stage. In addition, the regeneration system that obtained more bulblets showed significantly higher expression of LsCWIN2 than those that obtained fewer bulblets. Our data demonstrate the essential role of BA in accelerating sucrose degradation and the selection of a dominant sucrose cleavage pattern at the competence stage of in vitro bulblet regeneration. We propose that a relatively active CWIN-catalyzed pathway at the competence stage might promote bulblet regeneration, thus influencing bulb yield.

Full-length transcriptome analysis revealed that 2,4-dichlorophenoxyacetic acid promoted in vitro bulblet initiation in lily by affecting carbohydrate metabolism and auxin signaling

“…In Lilium , the enzymes involved in starch synthetic direction, such as AGPase, GBSS, SS, and SBE, showed a decreasing trend in mother scales but an increasing trend in bulblets during bulblet formation ( Li et al., 2014 ; Wu et al., 2021 ). Moreover, starch content in basal scales and basal plates of Lycoris (the major sites of bulblet regeneration) showed a rapid decline during bulblet initiation in the efficient bulblet regeneration system ( Ren et al., 2021 ). Here, we found in the 2,4-D-treated group, the more efficient group for in vitro bulblet initiation, key enzymes involved in starch synthesis (AGPL, SS and GBSS) were downregulated, while key enzymes involved in starch degradation (AMY and BAM) were upregulated compared to the control group ( Figures 6B, C ).…”

“…In this study, 16 SUSs in Lbg and 17 SUSs in Lb were upregulated at 1 DAT or 8 DAT, and one CWIN in Lbg and two CWINs in Lb were upregulated at 1 DAT and then downregulated ( Figures 6B, C ). For example, SUS and CWIN often presented an opposite expression pattern during bulblet initiation, and this change was considered to be a possible sign of the transition from bulblet initiation to development ( Ren et al., 2021 ; Wu et al., 2021 ). In particular, CWINs were highly expressed during the early bulblet initiation stage and produced glucose, which might act as sugar signaling rather than carbon resources ( Wu et al., 2021 ).…”

“…A clear shift was observed from CWIN-catalyzed to SUS-catalyzed sucrose cleavage patterns, meanwhile, sucrose unloading pathway changed from apoplasmically to symplasimically at the key shoot-to-bulblet transition stage in Lilium Oriental Hybrids ‘Sorbonne’ ( Wu et al., 2021 ). Similarly, CWIN and SUS exhibited exactly opposite expression patterns during the competence stage of bulblet regeneration in Lycoris ( Ren et al., 2021 ). The above results indicated that the transition from bud initiation to bulblet enlargement was usually accompanied by the change of dominant sucrose unloading pathway.…”

Transcriptome-wide characterization of bHLH transcription factor genes in Lycoris radiata and functional analysis of their response to MeJA

“…Besides, key functional genes involved in anthocyanin metabolism during flower development in L. radiata have also been characterized ( Wang et al., 2021 ). Moreover, a relatively active cell wall invertase (CWIN)-catalyzed apoplasmic sucrose cleavage pattern at the competence stage have been found to increase L. sprengeri bulblet regeneration ( Ren et al., 2021 ), and the mode of sucrose degradation could be identified as a metabolic marker for early vegetative propagation in bulbs of Lycoris ( Ren et al., 2022 ). Considering transcription factors (TF) are important gene expression switches that activate or repress the expression of specific target genes by interacting with cis -elements in the gene promoter region, regulating various biological processes including plant development, growth, biosynthesis of secondary metabolites, and response to stresses ( Sun et al., 2018 ), it is necessary to investigate whether and how TFs participate the biological processes in Lycoris plants.…”

Comparative transcriptome and metabolome analyses identified the mode of sucrose degradation as a metabolic marker for early vegetative propagation in bulbs of Lycoris

“…It is generally agreed that higher expression of genes in the sucrose degrading pathway, such as those encoding SUS and invertase (INV), is beneficial for the early formation of regenerated propagules (Gao et al., 2018 ; Li et al., 2014 ; Xu et al., 2020 ), whereas increased expression of genes involved in the starch synthetic direction, including those encoding soluble starch synthase, starch branching enzyme, ADP‐glucose pyrophosphorylase and granule‐bound starch synthase, proceeds with filling of storage compounds (Li et al., 2014 ; Wu et al., 2021 ; Xu et al., 2020 ). Our recent study revealed that early sucrose degradation and the dominant sucrose cleavage pattern influence L. sprengeri bulblet regeneration in vitro (Ren, Xu, et al., 2021 ). However, the molecular mechanisms underlying early sucrose metabolism that may affect regeneration capacities during VP still remain to be explored.…”