Abstract
Background: Cymbidium goeringii is one of the most horticulturally important and popular ornamental plants in the orchid family (Orchidaceae). It blooms in winter during January-March and a period of low temperature is necessary for its normal flowering, otherwise there is flower bud abortion, which seriously affects the economic benefits. However, the molecular mechanism underlying winter-blooming behavior in C. goeringii is unclear. Results: In this research, we firstly study the flowering physiology of C. goeringii by cytobiology observations and physiological experiments. Using comparative transcriptome analysis, we identified 582 differentially expressed unigenes responding to cold treatment that were involved in metabolic process, flowering time, hormone signaling, stress response, and cell cycle, implying their potential roles in regulating winter-blooming of C. goeringii. Twelve MADS-box genes among them were investigated by full-length cDNA sequence analysis and expression validation, which indicated that three genes within the SHORT VEGETATIVE PHASE (SVP) sub-group had the most significant repressed expression after cold treatment. Further analysis revealed that the SVP genes showed population variation in expression that correlated with cold-regulated flowering and responded to low temperature earlier than the flowering pathway integrators CgAP1, CgSOC1, and CgLFY, suggesting a potential role of CgSVP genes in the early stage of low-temperature-induced blooming of C. goeringii. Moreover, a yeast two-hybrid experiment confirmed that CgSVP proteins interacted with CgAP1 and CgSOC1, suggesting that they may synergistically control the process of C. goeringii flowering in winter. Conclusions: This study represents the first exploration of flowering physiology of C. goeringii and provides gene expression information that could facilitate our understanding of molecular regulation of orchid plant winter-flowering, which could provide new insights and practical guidance for improving their flowering regulation and molecular breeding.