Integrative Targeted Metabolomics and Transcriptomics Reveal the Mechanism of Leaf Coloration in Impatiens hawkeri ‘Sakimp005’

One of the most important characteristics of ornamental plants is leaf color, which enhances the color of plant landscapes and attracts pollinators for reproduction. The leaves of <i>Impatiens hawkeri</i> 'Sakimp005' are initially green, then the middle part appears yellow, then gradually become white, while the edge remains green. In the study, leaves of <i>I. hawkeri</i> 'Sakimp005', in four developmental stages (S1-G, S2-C, S3-C, and S4-C), were selected for the determination of pigment content, chromaticity values, integrative metabolomics, and transcriptomics analyses. The carotenoid content of leaves varied significantly and regularly at four stages, and the colorimetric values corroborated the phenotypic observations. The results of integrative metabolomics and transcriptomics analysis show that the accumulation of two carotenoids (lutein and zeaxanthin), to different degrees in the leaves of <i>I. hawkeri</i> 'Sakimp005' at four stages, led to the vary yellowing phenomenon. We speculated that the carotenoid biosynthesis (containing two branches: α-branch and β-branch) in leaves by <i>IhLUT1</i> and <i>IhLUT5</i> in the α-branch and <i>IhBCH2</i> genes in the β-branch differed. These findings provide a molecular basis for <i>Impatiens</i> plants' leaf color breeding and improve the knowledge of the leaf color mechanism.