Genome-wide identification and analysis of carotenoid synthesis-related R2R3-MYB genes in Rhododendron molle G. Don

Yellow flower coloration is a key trait of high value in the ornamental horticulture industry. Rhododendron molle G. Don, a deciduous species prized for its distinctive yellow blooms and bioactive compounds, is a valuable resource for breeding and medicinal applications. β-carotene has been established as the primary pigment responsible for yellow coloration in R. molle petals, and RmLCYB is a key candidate gene in the carotenoid biosynthesis pathway. However, the molecular mechanism controlling the accumulation of β-carotene in R. molle flowers is still unclear, and the information about R2R3-MYB genes in R. molle is limited. In this study, 106 RmR2R3-MYB genes were identified and divided into 31 subgroups. RNA-seq analysis characterized the expression profiles of differentially expressed genes including R2R3-MYB and carotenoid biosynthesis genes. Subsequently, quantitative real-time PCR validation highlighted seven critical carotenoid biosynthesis genes and five differentially expressed RmMYBs . Expression correlation analysis revealed that RmMYB90 was positively correlated with RmLCYB2 , whereas RmMYB28 and RmMYB100 were negatively correlated. Yeast one-hybrid and dual-LUC assays demonstrated that RmMYB100 directly binds to the RmLCYB2 promoter and represses its transcription. This study provides the first functional insight into the R2R3-MYB family in R. molle and identifies candidate regulators of carotenoid synthesis. These candidate regulators provide targets for further functional characterization and may guide breeders in developing new ornamental cultivars with manipulated carotenoid yield and composition.