Effects of Exogenous MeJA and BR treatments on leaf color and anthocyanin synthesis gene expression in Aeonium arboreum 'Halloween'

To investigate the regulatory effects of methyl jasmonate (MeJA) and brassinosteroid (BR) co-treatment on leaf color in Aeonium arboreum 'Halloween' and to identify key differentially expressed genes involved in anthocyanin biosynthesis, this study preliminarily explored the molecular mechanism underlying exogenous hormone-induced leaf color change in Aeonium succulent plants. One-year-old stem cuttings of 'Halloween' were sprayed with a mixture of 40 mg/L MeJA and 0.04 mg/L BR for 42 consecutive days. Leaf color parameters, anthocyanin content, and expression levels of anthocyanin synthesis-related genes were measured in functional leaves. After 14 ～ 42 days of treatment, leaves of the experimental group (EG) turned from green to purplish-red. From 28 to 42 days, the leaf color parameters L* (brightness), a* (red/green axis), and c* (saturation) were increased significantly (P < 0.05). Anthocyanin content in EG was significantly increased (P < 0.05) between 14 to 28. qRT-PCR analysis revealed that most structural genes (AaCHS2, AaCHI1, AaF3'H, AaUFGT4) in the anthocyanin pathway were up-regulated after 42 days. Notably, the expression levels of transcription factors AaMYB113 and AaMYB114 were significantly induced, reaching 2.20-fold (P < 0.05) and 47.96-fold (P < 0.001) of CK levels, respectively. These findings suggest that the synergistic effect of MeJA and BR was demonstrated to effectively induce purplish-red leaf coloration in 'Halloween'. This mechanism may involve activation of anthocyanin synthesis-related structural genes and transcription factors AaMYB113 and AaMYB114.¹