Abstract
BackgroundSweet osmanthus (Osmanthus fragrans Lour.) is one of the top ten traditional ornamental flowers in China. The flowering time of once-flowering cultivars in O. fragrans is greatly affected by the relatively low temperature, but there are few reports on its molecular mechanism to date. A hypothesis had been raised that genes related with flower opening might be up-regulated in response to relatively low temperature in O. fragrans. Thus, our work was aimed to explore the underlying molecular mechanism of flower opening regulated by relatively low temperature in O. fragrans.ResultsThe cell size of adaxial and abaxial petal epidermal cells and ultrastructural morphology of petal cells at different developmental stages were observed. The cell size of adaxial and abaxial petal epidermal cells increased gradually with the process of flower opening. Then the transcriptomic sequencing was employed to analyze the differentially expressed genes (DEGs) under different number of days’ treatments with relatively low temperatures (19 °C) or 23 °C. Analysis of DEGs in Gene Ontology analysis showed that “metabolic process”, “cellular process”, “binding”, “catalytic activity”, “cell”, “cell part”, “membrane”, “membrane part”, “single-organism process”, and “organelle” were highly enriched. In KEGG analysis, “metabolic pathways”, “biosynthesis of secondary metabolites”, “plant-pathogen interaction”, “starch and sucrose metabolism”, and “plant hormone signal transduction” were the top five pathways containing the greatest number of DEGs. The DEGs involved in cell wall metabolism, phytohormone signal transduction pathways, and eight kinds of transcription factors were analyzed in depth.ConclusionsSeveral unigenes involved in cell wall metabolism, phytohormone signal transduction pathway, and transcription factors with highly variable expression levels between different temperature treatments may be involved in petal cell expansion during flower opening process in response to the relatively low temperature. These results could improve our understanding of the molecular mechanism of relatively-low-temperature-regulated flower opening of O. fragrans, provide practical information for the prediction and regulation of flowering time in O. fragrans, and ultimately pave the way for genetic modification in O. fragrans.
Highlights
Sweet osmanthus (Osmanthus fragrans Lour.) is one of the top ten traditional ornamental flowers in China
The developing petals of carnation show high activities of cellulase and pectin esterase [11]. These findings reveal that petal growth relevant to flower opening is probably attributed to cell expansion
Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis Developmental stages of sweet osmanthus flowers for SEM and TEM analysis were described as follows: stage 1 (S1), the outer bud scales unfurled and the inner bud scales still furled; S2, the bud became globular-shaped and the inside bracts covering the inflorescence was visible; S3, the inflorescence burst through bracts and the florets closely crowded; S4, initial flowering stage; S5, full flowering stage; S6, pollen-scattered stage
Summary
Sweet osmanthus (Osmanthus fragrans Lour.) is one of the top ten traditional ornamental flowers in China. The flowering time of once-flowering cultivars in O. fragrans is greatly affected by the relatively low temperature, but there are few reports on its molecular mechanism to date. Our work was aimed to explore the underlying molecular mechanism of flower opening regulated by relatively low temperature in O. fragrans. (Oleaceae) is one of the top ten traditional ornamental plants in China with more than 2500 years’ history of cultivation [1]. The researches on the flowering time of different cultivars indicated that relatively low temperature before blooming is the most important environmental factor determining the flower opening of O. fragrans [3, 4]. The knowledge of molecular mechanism of flower opening in O. fragrans, especially response to relatively low temperature, still remains limited
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