Objective To identify members of the R2R3-MYB gene family (named CiaMYB) in Chrysanthemum indicum var. aromaticum, a folk medicinal plant from Shennongjia, analyze their genetic evolutionary characteristics and expression patterns in response to UV-B stress, and explore the molecular mechanisms by which they regulate flavonoid synthesis. Methods Based on the whole-genome sequence of C. indicum var. aromaticum, bioinformatics analyses were performed to comprehensively identify CiaMYB members, and systematic analyses were conducted on their protein physicochemical properties, chromosomal localization, gene structure, collinearity relationships, and composition of cis-acting elements. Combined with transcriptome sequencing and correlation analysis, CiaMYB genes involved in flavonoid biosynthesis were screened. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to verify the expression patterns of key genes, and the functional localization of the proteins was analyzed. Results A total of 140 CiaMYB genes were identified, encoding hydrophilic proteins consisting of 206—868 amino acids, which are unevenly distributed on nine chromosomes. The promoter regions are enriched with cis-acting elements related to light response, abscisic acid (ABA) and methyl jasmonate (MeJA) signaling pathways. UV-B irradiation significantly induces differential expression of CiaMYB genes and accumulation of total flavonoids in leaves. Among them, CiaMYB040 and CiaMYB066 are highly homologous to the S7 subfamily, which is critical for flavonol synthesis in Arabidopsis thaliana, and their expression levels show a strong positive correlation with total flavonoid content, suggesting that they play a key transcriptional regulatory role in the flavonoid synthesis pathway. Subcellular localization confirmed that CiaMYB040 and CiaMYB066 proteins are localized in the nucleus. Conclusion This study is the first to systematically reveal the evolutionary characteristics of R2R3-MYB family members in C. indicum var. aromaticum, and preliminarily screen CiaMYB genes that respond to UV-B stress and are involved in regulating flavonoid synthesis. It provides important candidate gene resources for elucidating the molecular mechanism of plant high-altitude stress adaptation, as well as for flavonoid metabolism regulation and stress-resistant genetic improvement in Asteraceae plants.

Chrysanthemum indicum var. aromaticum L.  /  R2R3-MYB  /  transcriptional regulation  /  UV-B  /  flavonoid metabolism