Abstract
The bicolor Asiatic hybrid lily cultivar “Tiny Padhye” is an attractive variety because of its unique color pattern. During its bicolor tepal development, the upper tepals undergo a rapid color change from green to white, while the tepal bases change from green to purple. However, the molecular mechanisms underlying these changes remain largely uncharacterized. To systematically investigate the dynamics of the lily bicolor tepal transcriptome during development, we generated 15 RNA-seq libraries from the upper tepals (S2-U) and basal tepals (S1-D, S2-D, S3-D, and S4-D) of Lilium “Tiny Padhye.” Utilizing the Illumina platform, a total of 295,787 unigenes were obtained from 713.12 million high-quality paired-end reads. A total of 16,182 unigenes were identified as differentially expressed genes during tepal development. Using Kyoto Encyclopedia of Genes and Genomes pathway analysis, candidate genes involved in the anthocyanin biosynthetic pathway (61 unigenes), and chlorophyll metabolic pathway (106 unigenes) were identified. Further analyses showed that most anthocyanin biosynthesis genes were transcribed coordinately in the tepal bases, but not in the upper tepals, suggesting that the bicolor trait of “Tiny Padhye” tepals is caused by the transcriptional regulation of anthocyanin biosynthetic genes. Meanwhile, the high expression level of chlorophyll degradation genes and low expression level of chlorophyll biosynthetic genes resulted in the absence of chlorophylls from “Tiny Padhye” tepals after flowering. Transcription factors putatively involved in the anthocyanin biosynthetic pathway and chlorophyll metabolism in lilies were identified using a weighted gene co-expression network analysis and their possible roles in lily bicolor tepal development were discussed. In conclusion, these extensive transcriptome data provide a platform for elucidating the molecular mechanisms of bicolor tepals in lilies and provide a basis for similar research in other closely related species.
Highlights
(Lilium spp.) is one of the most important ornamental plants because of their large flowers with unique and diverse colors
As that study did not provide a global view of transcriptome dynamics over the key tepal developmental stages of anthocyanin biosynthesis, it was hard to perform a co-expression network analysis to identify new candidate target genes
We analyzed the global transcription of pigmented and nonpigmented tepal parts from “Tiny Padhye” at stage 2 and constructed a high-resolution transcriptome atlas of lily inner tepal development using a time series of tepal base samples taken from Stage 1 (S1) to stage 4 (S4)
Summary
(Lilium spp.) is one of the most important ornamental plants because of their large flowers with unique and diverse colors. A typical ornamental feature of Asiatic hybrid lilies is the variety of flower colors, including yellows, oranges, pinks, reds, and whites. In addition to the various colors, Asiatic hybrid lilies exhibit variations in pigmentation patterns, including spots and bicolors. Post-transcriptional gene silencing (PTGS) of chalcone synthase (CHS) genes in non-pigmented areas produces the white areas of bicolor flower petals in several horticultural crops, such as petunia (Petunia hybrida) (Koseki et al, 2005; Saito et al, 2006; Morita et al, 2012), camellia (Camellia japonica) (Tateishi et al, 2010), and dahlia (Dahlia variabilis) (Ohno et al, 2011). Two types of bicolor flowers are found in Asiatic hybrid lilies; in one type, anthocyanins accumulate in the upper tepals (e.g., “Lollipop”) while in the other type, anthocyanin pigments accumulate in the tepal bases (e.g., “Tiny Padhye”). Whether the same molecular mechanisms underlie the second type of bicolor tepals remains unclear
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