De Novo Transcriptomics Analysis of the Floral Scent of Chinese Narcissus

The Chinese narcissus is a well-known monocotyledon plant with a beautiful color, and fresh with a sweet floral scent. Lack of transcriptomic and genomic information hinders understanding of the molecular mechanisms underlying the biosynthesis of narcissus floral scent volatiles. Here we predicted the functions of identified significantly differentially expressed genes (DEGs), according to public protein annotation databases. Using RNA-sequencing (RNA-Seq) on the Illumina HiSeq system and de novo transcriptome assembly, we investigated gene expression in narcissus corona and petal tissues at the early flowering (day 1) and full-bloom (day 7) stages. Significant differences in the expression profiles of 14 fragrance-related genes were further analyzed by qRT-PCR. A total of 62,826,860,514 bases were generated by RNA-seq; clean reads were 210,658,254 bp, and the guanine-cytosine content was 47.7%-48.88%. Transcripts (n = 167,374; 67.27%) and unigenes (n = 81,442; 32.73%) had mean lengths of 1069.70 bp and 813.27 bp, respectively. The total length and N50 length values of transcripts were 179,040,048 bp and 1654 bp, while those of unigenes were 66,234,291 bp and 1406 bp. Assembled genes were annotated by comparison with the non-redundant, Protein family, Clusters of Orthologous Groups of proteins, Swiss-Prot, Kyoto Encyclopedia of Genes and Genomes, and Gene Ontology, public protein databases. Additionally, 46 and 71 significantly differentially expressed genes encoded enzymes and transcription factors, respectively, associated with floral volatiles biosynthesis pathways, were analyzed in-depth. Our findings represent a fundamental step toward better understanding of the mechanisms of narcissus floral volatile biosynthesis.