Abstract
The golden camellia, Camellia nitidissima Chi., is a well-known ornamental plant that is known as “the queen of camellias” because of its golden yellow flowers. The principal pigments in the flowers are carotenoids and flavonol glycosides. Understanding the biosynthesis of the golden color and its regulation is important in camellia breeding. To obtain a comprehensive understanding of flower development in C. nitidissima, a number of cDNA libraries were independently constructed during flower development. Using the Illumina Hiseq2500 platform, approximately 71.8 million raw reads (about 10.8 gigabase pairs) were obtained and assembled into 583,194 transcripts and 466, 594 unigenes. A differentially expressed genes (DEGs) and co-expression network was constructed to identify unigenes correlated with flower color. The analysis of DEGs and co-expressed network involved in the carotenoid pathway indicated that the biosynthesis of carotenoids is regulated mainly at the transcript level and that phytoene synthase (PSY), β -carotene 3-hydroxylase (CrtZ), and capsanthin synthase (CCS1) exert synergistic effects in carotenoid biosynthesis. The analysis of DEGs and co-expressed network involved in the flavonoid pathway indicated that chalcone synthase (CHS), naringenin 3-dioxygenase (F3H), leucoanthocyanidin dioxygenase(ANS), and flavonol synthase (FLS) play critical roles in regulating the formation of flavonols and anthocyanidin. Based on the gene expression analysis of the carotenoid and flavonoid pathways, and determinations of the pigments, we speculate that the high expression of PSY and CrtZ ensures the production of adequate levels of carotenoids, while the expression of CHS, FLS ensures the production of flavonols. The golden yellow color is then the result of the accumulation of carotenoids and flavonol glucosides in the petals. This study of the mechanism of color formation in golden camellia points the way to breeding strategies that exploit gene technology approaches to increase the content of carotenoids and flavonol glucosides and to decrease anthocyanidin synthesis.
Highlights
The camellia, a traditional and much-loved flower in China, is a well-known and popular ornamental plant around the world
To obtain an overview of the flower transcriptome of C. nitidissima at different developmental stages, RNA-seq strandspecific libraries from three biological replicates of C. nitidissima plants sampled at five developmental stages (15 libraries in total) were prepared for transcriptome analysis
Three assemblers were compared with each other and the results showed that Trinity platform performed better in both count of full transcripts, remapped reads ratio and the completeness of transcriptome (Suplementary Tables 3, 4)
Summary
The camellia, a traditional and much-loved flower in China, is a well-known and popular ornamental plant around the world. The golden camellia, Camellia nitidissima Chi., known as “the queen of camellias” or “dreaming camellia” because of its golden yellow flowers, Chang and Ren (1998)and Gao (2005) is a highly-prized plant that is found naturally in the Guangxi Zhuang Autonomous Region of China. Since it was first discovered in the 1960s, this rare and unique genetic resource has been used in attempts to breed yellow camellia cultivars (Chen, 1987). One reason for the slow progress in the use of the golden camellia in hybrid breeding is that the biosynthesis of the golden yellow color and its regulation remain unclear, and as a result informed breeding programs cannot be pursued
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