Molecular characterization of carotenoid biosynthetic genes and carotenoid accumulation in Scutellaria baicalensis Georgi

Scutellaria baicalensis has a wide range of biological activities and has been considered as an important traditional drug in Asia and North America for centuries. A partial-length cDNA clone encoding phytoene synthase (SbPSY) and full-length cDNA clonesencoding phytoene desaturase (SbPDS), ξ-carotene desaturase (SbZDS), β-ring carotene hydroxylase (SbCHXB), and zeaxanthin epoxidase (SbZEP)were identifiedin S. baicalensis. Sequence analyses revealed that these proteins share high identity and conserved domains with their orthologous genes. SbPSY, SbPDS, SbZDS, SbCHXB, and SbZEP were constitutively expressed in the roots, stems, leaves, and flowers of S.baicalensis. SbPSY, SbPDS, and SbZDS were highly expressed in the stems, leaves, and flowers and showed low expression in the roots, where only trace amounts of carotenoids were detected. SbCHXB and SbZEP transcripts were expressed at relatively high levels in the roots, stems, and flowers and were expressed at low levels in the leaves, where carotenoids were mostly distributed. The predominant carotenoids in S.baicalensiswere lutein and β-carotene, with abundant amounts found in the leaves (517.19 and 228.37 μg g(-1) dry weight, respectively). Our study on the biosynthesis of carotenoids in S. baicalensis will provide basic data for elucidating the contribution of carotenoids to the considerable medicinal properties of S. baicalensis.