Tree peony PsMYB44 negatively regulates petal blotch distribution by inhibiting dihydroflavonol-4-reductase gene expression


 
 
 Tree peony (Paeonia suffruticosa Andr.) has been widely cultivated as a field plant, and petal blotch is one of its important traits, which not only promotes proliferation but also confers high ornamental value. However, the regulatory network controlling blotch formation remains elusive due to the functional differences and limited conservation of transcriptional regulators in dicots.
 
 
 
 We performed phylogenetic analysis to identify MYB44-like transcription factors in P. suffruticosa blotched cultivar ‘High noon’ petals. A candidate MYB44-like transcription factor PsMYB44 was analyzed via expression pattern analysis, subcellular localization, target gene identification, gene silencing in P. suffruticosa petals and heterologous overexpression in tobacco.
 
 
 
 A blotch formation-related MYB44-like transcription factor PsMYB44 was cloned. The C-terminal of the PsMYB44 amino acid sequence had a complete C2 motif that affects anthocyanin biosynthesis, and PsMYB44 was clustered in the MYB44-like transcriptional repressor branch. PsMYB44 was located in the nucleus, and its spatial and temporal expression patterns negatively correlated with the blotch formation. Furthermore, a yeast one-hybrid assay showed that PsMYB44 could target the promoter of the late anthocyanin biosynthesis-related dihydroflavonol-4-reductase (DFR) gene, and a dual-luciferase assay demonstrated that PsMYB44 could repress PsDFR promoter activity. On the one hand, overexpression of PsMYB44 significantly faded the red color of tobacco flowers and decreased the anthocyanin content by 42.3% by downregulating the expression level of the tobacco NtDFR gene. On the other hand, PsMYB44-silenced P. suffruticosa petals had a redder blotch color, which was attributed to the fact that silencing PsMYB44 redirected metabolic flux to the anthocyanin biosynthesis branch, thereby promoting more anthocyanin accumulation in the petal base.
 
 
 
 These results demonstrated that PsMYB44 negatively regulated the biosynthesis of anthocyanin by directly binding to the PsDFR promoter and subsequently inhibiting the blotch formation, which helped to elucidate the molecular regulatory network of anthocyanin-mediated blotch formation in plants.
