Genome-wide identification of MYB transcription factors in Rheum officinale Baill. and their responses to UV-B and MeJA treatment

BACKGROUND: Rheum officinale Baill., a foundational plant in traditional Chinese medicine, whose roots and rhizomes exhibit significant pharmacological activities primarily attributed to anthraquinones and other bioactive compounds. However, the transcriptional regulatory mechanisms underlying anthraquinone biosynthesis are not well understood, and the key regulatory factors require further investigation. MYB transcription factors play central roles in secondary metabolism and stress signaling, suggesting their potential involvement in anthraquinone regulation, particularly in response to environmental cues such as UV-B radiation and hormonal signals like methyl jasmonate (MeJA). RESULTS: We performed a genome-wide identification of MYB genes in R. officinale, identifying 237 RoMYBs, including 150 R2R3-MYBs, 81 R1-MYBs, four 3R-MYBs, and two atypical members. Phylogenetic, structural, and evolutionary analyses revealed conserved subfamily organization and gene family expansion driven primarily by segmental duplication. Notably, UV-B treatment significantly induced the accumulation of several anthraquinones, including rhein and emodin, in a time-dependent manner. Expression profiling identified RoMYBs responsive to both MeJA and UV-B, with RoMYB128 and RoMYB134 showing consistent upregulation that correlated with anthraquinone accumulation. Co-expression analysis further revealed that these two genes strongly correlated with multiple CHS-related structural genes in the anthraquinone biosynthetic pathway. Subcellular localization analysis confirmed nuclear localization of both proteins, and transcriptional activity assays revealed that RoMYB128 functions as a transcriptional activator. CONCLUSIONS: This study provides the first comprehensive genomic overview of the MYB family in R. officinale and highlights candidate regulators that integrate light and hormone signaling to modulate anthraquinone biosynthesis, thereby offering a foundation for future mechanistic studies and metabolic engineering efforts.