Integrative Analysis of Metabolome and Transcriptome Revealed Lutein Metabolism Contributed to Yellow Flower Formation in .

is a famous ornamental woody tree with colorful flowers. with yellow flowers is one of the most precious varieties. Regretfully, metabolites and regulatory mechanisms of yellow flowers in are still unclear. This hinders innovation of flower color breeding in . To elucidate the metabolic components and molecular mechanisms of yellow flowers, we analyzed transcriptome and metabolome between 'HJH' with yellow flowers and 'ZLE' with white flowers. Comparing the metabolome of the two varieties, we determined that carotenoids made contributions to the yellow flowers rather than flavonoids. Lutein was the key differential metabolite to cause yellow coloration of 'HJH'. Transcriptome analysis revealed significant differences in the expression of carotenoid cleavage dioxygenase () between the two varieties. Specifically, the expression level of was higher in 'ZLE' than that in 'HJH'. Moreover, we identified six major transcription factors that probably regulated to affect lutein accumulation. We speculated that carotenoid cleavage genes might be closely related to the yellow flower phenotype in . Further, the coding sequence of has been cloned from the 'HJH' petals, and bioinformatics analysis revealed that PmCCD4 possessed conserved histidine residues, ensuring its enzymatic activity. PmCCD4 was closely related to PpCCD4, with a homology of 98.16%. Instantaneous transformation analysis in petal protoplasts of revealed PmCCD4 localization in the plastid. The overexpression of significantly reduced the carotenoid content in tobacco plants, especially the lutein content, indicating that lutein might be the primary substrate for PmCCD4. We speculated that might be involved in the cleavage of lutein in plastids, thereby affecting the formation of yellow flowers in . This work could establish a material and molecular basis of molecular breeding in for improving the flower color.