Abstract
Flower color serves as a pivotal ornamental trait in plants, significantly impacting their aesthetic value. H macrophylla is particularly esteemed for its large, vibrant flowers and the remarkable variability in color it exhibits. In this study, the MYB gene family within H. macrophylla was comprehensively examined, resulting in the identification of 72 MYB genes through genomic screening utilizing the Hidden Markov Model (HMM) method. A physicochemical analysis revealed a diverse range of properties among these proteins, with sizes varying from 65 to 770 amino acids; notably, six of these proteins were classified as stable. Predominantly, MYB proteins were localized within the nucleus, although some were also detected in other organelles, indicating a multifaceted role in cellular function. Phylogenetic analysis established that 13 MYB genes from H. macrophylla can be categorized into five distinct subfamilies based on the classifications observed in Arabidopsis thaliana, suggesting their involvement in the biosynthetic pathways of anthocyanins and proanthocyanidins. Expression analysis indicated a significant correlation between specific R2R3-MYB transcription factors, particularly HmMYB54, and the accumulation of anthocyanins during various flowering stages. qPCR results showed that the expression of HmMYB54 was consistent with the accumulation trend of 'Forever Summer' colors in hydrangea, while HmMYB61 was just the opposite, which was consistent with RNAseq, suggesting that they regulated the formation of 'Foever Summer' blue flowers positively and negatively, respectively. A proposed regulatory model has been articulated to elucidate the mechanisms by which these MYB genes affect flower color, particularly through their interactions with essential structural genes in the anthocyanin biosynthesis pathway. Thus, this study not only enhances the understanding of the genetic basis of flower coloration in H. macrophylla but also highlights the adaptive significance of MYB transcription factors in response to environmental challenges.