CPTA treatment reveals potential transcription factors associated with carotenoid metabolism in flowers of Osmanthus fragrans

Osmanthus fragrans is one of the top ten traditional flowers in China. It is divided into three different groups according to its color. α-Carotene and β-carotene are the main determinants to distinguish the color differences between three groups. However, the dominant genes and transcription factors involved in carotenoid metabolism remain unclear. CPTA treatment (0.7 mmol · L−1) remarkably promoted lycopene, α-carotene and β-carotene contents in flowers. Transcriptome sequencing analysis revealed that CPTA treatment could trigger chain reactions in carotenoid metabolism pathway genes. Four up-regulated and 10 down-regulated transcription factors which have close association with carotenoid variation were significantly induced by CPTA treatment. The up-regulated TFs such as MYB43, MYB123, HSF, were further subjected to transcript expression determination in different cultivars with drastic colors. Among them, transcript expression of four up-regulated TFs coincided with the carotenoid accumulation in different cultivars. We selected up-regulated OfMYB43 to verify its function, which is related to stress tolerance and transcriptional regulation. Transient overexpression of OfMYB43 in O. fragrans flowers showed that it could remarkably promote the expression of PDS, ZISO, LCYE and CCD4, leading to increased accumulation of β-branch carotenoids. OfMYB43 was a potential positive regulator of carotenoid biosynthesis in O. fragrans flowers. This study provides insight into the molecular mechanism of carotenoid metabolism in O. fragrans.