Transcriptomic investigation of the basis of Corona and petal colour in Chinese narcissus

Chinese narcissus is a traditional flower with gorgeous corona and petal colour. The carotenoid biosynthesis pathway is primarily responsible for colour formation in narcissus flower. However, the role of carotenoid biosynthesis enzymes and intermediates in colour development, and the molecular basis of differences between orange-yellow corona and milky-white petals are unclear. Here, we performed RNA-Seq using Illumina HiSeq platform and de novo transcriptome assembly to predict the functions of the identified significantly differentially expressed genes (DEGs). We investigated genes expression in narcissus corona and petal tissues on the first and seventh day of flowering. 14 colour -related genes were further analysed by qRT-PCR. The significantly DEGs encoded various kinds of enzymes and transcription factors (TFs) associated with carotenoid and flavonoid biosynthesis pathways, respectively. These DEGs mainly included phytoene synthase (PSY) gene, lycopene epsilon cyclase (LCYE) gene, β-carotene hydroxylase (BCH) gene, β-carotene isomerase gene and AP2/ ERF, B3, MYB, NAC and WRKY TFs. Additionally, an in-depth analysis of chlorophyll biosynthesis and degradation pathways was performed. These results enhance our understanding of the mechanism of colour formation in narcissus flower and provide a basis for further investigation of the functions of proteins encoded by the annotated unigenes and cDNA sequences of narcissus.