Abstract
BackgroundThe floral transition plays a vital role in the life of ornamental plants. Despite progress in model plants, the molecular mechanisms of flowering regulation remain unknown in perennial plants. Rosa chinensis ‘Old Blush’ is a unique plant that can flower continuously year-round. In this study, gene expression profiles associated with the flowering transition were comprehensively analyzed during floral transition in the rose.ResultsAccording to the transcriptomic profiles, 85,663 unigenes and 1,637 differentially expressed genes (DEGs) were identified, among which 32 unigenes were involved in the circadian clock, sugar metabolism, hormone, and autonomous pathways. A hypothetical model for the regulation of floral transition was proposed in which the candidate genes function synergistically the floral transition process. Hormone contents and biosynthesis and metabolism genes fluctuated during the rose floral transition process. Gibberellins (GAs) inhibited rose floral transition, the content of GAs gradually decreased and GA2ox and SCL13 were upregulated from vegetative (VM) meristem to floral meristem (FM). Auxin plays an affirmative part in mediating floral transition, auxin content and auxin-related gene expression levels were gradually upregulated during the floral transition of the rose. However, ABA content and ABA signal genes were gradually downregulated, suggesting that ABA passively regulates the rose floral transition by participating in sugar signaling. Furthermore, sugar content and sugar metabolism genes increased during floral transition in the rose, which may be a further florigenic signal that activates floral transition. Additionally, FRI, FY, DRM1, ELIP, COP1, CO, and COL16 are involved in the circadian clock and autonomous pathway, respectively, and they play a positively activating role in regulating floral transition. Overall, physiological changes associated with genes involved in the circadian clock or autonomous pathway collectively regulated the rose floral transition.ConclusionsOur results summarize a valuable collective of gene expression profiles characterizing the rose floral transition. The DEGs are candidates for functional analyses of genes affecting the floral transition in the rose, which is a precious resource that reveals the molecular mechanism of mediating floral transition in other perennial plants.
Highlights
The floral transition plays a vital role in the life of ornamental plants
Morphological description of the rose flowering transition Based on the morphological changes in the shoot apical meristem (SAM), we divided the continuous differentiation process from the vegetative to reproductive meristem into three stages in R. chinensis ‘Old Blush’ as follows: vegetative meristem (VM), pre-floral meristem (TM), and floral meristem (FM) (Fig. 1 and Additional file 1)
Functional enrichment of differentially expressed genes (DEGs) All DEGs were annotated using MapMan software, and this analysis indicated that DEGs in the comparison between VM and TM were enriched for RNA, hormone metabolism, signaling, and transport functions (Fig. 6c), indicating that plant hormone (GAs, auxin, and Abscisic acid (ABA)) signal transduction has a profound influence on the rose floral transition
Summary
The floral transition plays a vital role in the life of ornamental plants. Despite progress in model plants, the molecular mechanisms of flowering regulation remain unknown in perennial plants. Enormous progress has been made in research on the genetic, epigenetic and environmental factors that trigger the transition from vegetative growth to flowering in the model plant Arabidopsis thaliana. Environmental factors, photoperiod, and vernalization pathways mediate the transition to flowering in cooperation with diverse exogenous cues, including autonomous, gibberellin (GA), trehalose-6-phosphate (T6P), and age-dependent pathways [1, 2]. In combination, all these pathways converge to mediate a set of “floral integrator genes,”. Studies of annual plants cannot completely uncover the mechanisms of floral transition that underlie perennial plants, such as the rose recurrent flowering
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