Genome-wide analysis of R2R3-MYB transcription factors in Chrysanthemum seticuspe and C. morifolium and their roles in response to high-light stress.

Light is an important ecological factor limiting chrysanthemum cultivation, and the R2R3-MYB gene family plays a crucial role in resisting high light. Analyzing the gene structure of different ploidy species in the Chrysanthemum genus and the evolutionary relationships between species is essential for understanding the evolutionary patterns of the genes and genetic improvement. The study identified 236 and 732 MYB protein sequences from the genomes of diploid C. seticuspe and hexaploid C. morifolium, respectively. A phylogenetic tree was generated based on 168 MYB protein sequences from Arabidopsis thaliana, using a representative sequence from subfamily 6 as a reference point. Through BLASTP analysis, four MYB genes were identified in Chrysanthemum seticuspe, while nineteen were detected in the cultivar 'Zhongshanzigui' (C. morifolium). Motif analysis revealed that MYB proteins in C. seticuspe and C. morifolium possessed eight and nine conserved motifs, respectively. In C. seticuspe, three of the four MYB proteins retained all eight motifs, except for one lacking motif 4. Only nine out of nineteen MYB domains in C. morifolium displayed conservation, indicating a significant divergence from C. seticuspe. Promoter region analysis uncovered an abundance of light-responsive cis-elements, and qPCR assays demonstrated that MYB gene expression was upregulated under high-light conditions. Genomic mapping showed one tandemly repeated MYB gene in C. seticuspe, compared to four in C. morifolium. Comparative collinearity analysis indicated the absence of collinear gene pairs between A. thaliana and C. seticuspe but identified four orthologous MYB gene pairs shared between C. seticuspe and C. morifolium. No intraspecific collinearity was observed among the MYB genes in C. seticuspe. These findings suggest that gene duplication events, including genome triplication, have contributed to the structural complexity of the R2R3-MYB gene family in Chrysanthemum species. Such diversification has likely driven the expansion of metabolic pathways. This study provides new insights into the evolution and functional potential of MYB genes in C. seticuspe and C. morifolium, laying a foundation for future research in gene function, molecular breeding, and industrial applications of Chrysanthemum.