Transcriptomic and Physiological Analyses of Pigment Accumulation in Eucommia ulmoides ‘Hongye’

Eucommia ulmoides 'Hongye' is a new ornamental variety of E. ulmoides with excellent red or purple foliage.We found that E. ulmoides 'Hongye' exhibited a gradual change from green to red colour under light conditions.However, the colouring mechanism in the leaves of E. ulmoides 'Hongye' remains unclear.In this study, we compared the pigment content and leaf colour index of E. ulmoides 'Hongye' at five stages with those of E. ulmoides 'Xiaoye' , which was used as the control variety.The transcriptome sequencing data of the first-period (H1, green) and fifth-period (H5, red) leaves were also analysed and compared.The corresponding gene regulation in anthocyanin-related metabolic pathways was then analysed.Physiological results indicated that the contents of flavonoids and anthocyanins in red leaves (H5) were significantly higher than those in green leaves (H1), whereas the chlorophyll content in red leaves (H5) was lower than that in green leaves (H1).Moreover, the carotenoid content did not significantly differ between the two varieties.A transcriptome analysis identified 4240 differentially expressed genes (DEGs), and 20 of these genes were found to be involved in flavonoid and anthocyanin biosynthesis pathways.The results provide a reference for further study of the leaf colouration mechanism in E. ulmoides.