RhMYB1 and RhMYB123 form a positive feedback loop to regulate the proanthocyanidin biosynthesis in rose

Proanthocyanidins (PAs) are flavonoid-derived metabolites that make key contributions to plant and human health. Few studies have examined the mechanisms underlying the biosynthesis and accumulation of PAs in Rosa hybrida L. Here, we studied the role of the RhMYB1-RhMYB123 complex in regulating the biosynthesis of PAs in R. hybrida. The expression of PA biosynthesis genes was increased following overexpression of RhMYB123 in tobacco and rose somatic embryos, and this resulted in a marked increase in PA levels. Yeast two-hybrid assays showed that RhMYB123 interacted with RhMYB1, and these two proteins jointly promoted PAs biosynthesis by binding to the promoters of the genes encoding anthocyanin reductase (ANR) and leucoanthocyanidin reductase (LAR) for expression activation. Additional analysis showed that RhMYB1 could activate RhMYB123 expression through binding to related promoter and that the biosynthesis and accumulation of PAs are regulated by a positive feedback loop. Generally, the results of our study assist in better understanding the regulatory mech-anisms of PAs biosynthesis from new perspectives and have implications for the use of metabolic engineering to enhance the quality of rose plants.