Expanded functional roles of R2R3-MYB (S6) transcription factors in balancing phenylpropanoid and phenolamide pathways in Solanaceae

Events of duplication and neo/subfunctionalization have significantly expanded the functional roles of R2R3 myeloblastosis (MYB) transcription factors in plants. In a previous study, we demonstrated that two paralogous R2R3 MYBs from Solanum tuberosum and S. commersonii, AN1 and AN2, respectively, induce anthocyanin pigmentation to varying extents when transiently overexpressed. However, questions related to the distinct functions of these genes remained unanswered. In this study, we further investigated these genes by comparing transgenic tobacco plants that constitutively overexpress AN1 and AN2. We observed differences between AN1 and AN2 that not only influenced plant pigmentation but also impacted the structural features of vascular tissues. Both genes promoted the accumulation of phenolamides; however, AN1 showed a stronger capacity to regulate the phenylpropanoid pathway. In addition, our results suggest a potential role for AN2 in regulating additional biological processes potentially involved in vascular development, as indicated by the GUS promoter localization study. Collectively, these results shed new light on the potentially ancestral functions of these R2R3 MYB genes, extending their known impact beyond anthocyanin biosynthesis.