Flower colour is one of the crucial traits of ornamental plants. Rhododendron delavayi Franch. is a famous ornamental plant species distributed in the mountain areas of southwest China. This plant has red inflorescence and young branchlets. However, the molecular basis of the colour formation of R. delavayi is unclear. In this study, 184 MYB genes were identified based on the released genome of R. delavayi. These genes included 78 1R-MYB, 101 R2R3-MYB, four 3R-MYB and one 4R-MYB. The MYBs were divided into 32 subgroups by using phylogenetic analysis with those of Arabidopsis thaliana. The members of the same subgroup in R. delavayi had similar conserved domains and motifs, gene structures and promoter cis-regulatory elements, indicating their relative conserved function. In addition, transcriptome based on unique molecular identifier strategy and colour difference of the spotted petals, unspotted petals, spotted throat, unspotted throat and branchlet cortex were detected. Results showed significant differences in the expression levels of the R2R3-MYB genes. weighted co-expression network analysis between transcriptome and colour difference values showed that the MYBs were the most common transcription factors involved in colour formation, of which seven were R2-R3MYB and three were 1R-MYB. Two R2R3-MYB (DUH019226.1 and DUH019400.1) had the highest connectivity in the whole regulation network, which were identified as hub genes for the formation of red colour. These two MYB hub genes provide references for the study of transcriptional regulation of the formation of red colour of R. delavayi.
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