A complementary DNA library was constructed from the flowers ofChimonanthus praecox, an ornamental perennial shrub blossoming in winter in China. Eight hundred sixty-seven high-quality expressed sequence tag sequences with an average read length of 673.8 bp were acquired. A nonredundant set of 479 unigenes, including 94 contigs and 385 singletons, was identified after the expressed sequence tags were clustered and assembled. BLAST analysis against the nonredundant protein database and nonredundant nucleotide database revealed that 405 unigenes shared significant homology with known genes. The homologous unigenes were categorized according to Gene Ontology hierarchies (biological, cellular, and molecular). By BLAST analysis and Gene Ontology annotation, 95 unigenes involved in stress and defense and 19 unigenes related to floral development were identified based on existing knowledge. Twelve genes, of which 9 were annotated as “cold response,” were examined by real-time RT-PCR to understand the changes in expression patterns under cold stress and to validate the findings. Fourteen genes, including 11 genes related to floral development, were also detected by real-time RT-PCR to validate the expression patterns in the blooming process and in different tissues. This study provides a useful basis for the genomic analysis ofC. praecox.

Wintersweet (Chimonanthus praecox) is a woody garden plant with fragrant flowers, which blooms in deep winter. The vase life of fresh cut flowers is 8–9 days. We applied ethylene and 1-methylcyclopropene (1-MCP; an ethylene action inhibitor) to test the role of ethylene in flower opening and senescence. In addition, abscisic acid (ABA), gibberellic acid (GA3), two cytokinins, 6-benzylaminopurine (6-BA), and zeatin (ZT) were also applied. The expression pattern of CpSRG1, a senescence-related gene, was analyzed. Ethylene treatment accelerated flower opening and senescence, decreasing vase life by 2.1 days. It also decreased flower break strength, indicating the induction of abscission. 1-MCP slowed opening, delayed senescence, and prolonged vase life by 2.6 days. Ethylene dramatically induced the expression of the CpSRG1 gene, while 1-MCP suppressed it. ZT promoted flower opening and increased vase life by 1.6 days. It suppressed the expression of CpSRG1. 6-BA, GA3, or ABA had no significant effect on flower opening and senescence of wintersweet.

Plant senescence is a complex process that is controlled by developmental regulation and genetic programs. A senescence-related gene, CpSRG1, which belongs to the 2OG-Fe(II) dioxygenase superfamily, was characterized from wintersweet, and the phylogenetic relationship of CpSRG1 with homologs from other species was investigated. Tissue-specific expression analysis by qRT-PCR (quantitative real-time PCR) indicated that CpSRG1 is abundant in flower organs, especially in petals and stamen, and the highest CpSRG1 expression was detected in stage 6 (withering period) during flower development. The expression patterns of the CpSRG1 gene were further confirmed in CpSRG1pro::GUS (β-glucuronidase) plants, and the activity of the CpSRG1 promoter was enhanced by exogenous Eth (ethylene), SA (salicylic acid), and GA3 (gibberellin). Heterologous overexpression of CpSRG1 in Arabidopsis promoted growth and flowering, and delayed senescence. Moreover, the survival rates were significantly higher and the root lengths were significantly longer in the transgenic lines than in the wild-type plants, both under low nitrogen stress and GA3 treatment. This indicated that the CpSRG1 gene may promote the synthesis of assimilates in plants through the GA pathway, thereby improving growth and flowering, and delaying senescence in transgenic Arabidopsis. Our study has laid a satisfactory foundation for further analysis of senescence-related genes in wintersweet and wood plants. It also enriched our knowledge of the 2OG-Fe(II) dioxygenase superfamily, which plays a variety of important roles in this plant.